Former New England Patriots NFL football player Aaron Hernandez listens during his murder trial at the Bristol County Superior Court in Fall River, Mass., April 15, 2015.
Co-lead players' lawyer Christopher Seeger, left, and client former NFL player Shawn Wooden speak with members of the media after a hearing on the proposed NFL concussion settlement, Nov. 19, 2014, outside of the U.S. Courthouse in Philadelphia.
NFL Commissioner Roger Goodell speaks during his Press Conference two days before Super Bowl XLIX to be played at University off Phoenix Stadium in Glendale Arizona.
Charlotte Observer—MCT via Getty Images
NFL Hall of Famer Joe DeLamielleure talks about his recent diagnosis of a degenerative brain disease known as chronic traumatic encephalopathy, or CTE, in Charlotte, N.C., on Jan. 22, 2014.
Sarah Glenn—Getty Images
Quarterback Cardale Jones #12 of the Ohio State Buckeyes talks to the media after defeating the Oregon Ducks in the College Football Playoff National Championship Game at AT&T Stadium on January 12, 2015 in Arlington, Texas. The Ohio State Buckeyes defeated the Oregon Ducks 42 to 20.
Jeff Roberson / AP
Green Bay Packers quarterbacks Aaron Rodgers, left, and Matt Flynn, center, sit on the bench during the third quarter of an NFL preseason football game against the Indianapolis Colts in Indianapolis, Indiana on Aug. 26, 2011. Flynn, now a free agent, has been backing up Rodgers as a quarterback for the packers for several years.
The Washington Post—Getty Images
High school football in Lanham, MD. DuVal QB Antoine Brooks jr. (2) leaps for extra yardage during fourth quarter action against Wise on September 13, 2014
George Silk—Time & Life Pictures/Getty Images
On top of all of his NFL honors, Hall of Famer Frank Gifford holds two distinct pro football records: the most touchdowns (14) and the most interceptions (6) thrown by a non-quarterback in NFL history. But even those numbers indicate something remarkable about the man. As the Giants' Hall of Fame coach Steve Owens once said: "Gifford is one of the most versatile athletes I have ever seen. He has hard running ability. He is an accurate passer, a strong blocker, a sensational receiver, a superior defensive back and, with practice, he could become a consistent placekicker."
Linebacker Chris Borland walks on the practice field during the San Francisco 49ers' NFL football rookie camp in Santa Clara, Calif., May 23, 2014.
NFL commissioner Roger Goodell looks on as New England Patriots owner Robert Kraft speaks at an NFL press conference announcing new measures for the league's personal conduct policy during an owners meeting on Dec. 10, 2014, in Irving, Texas.
Dallas Cowboys running back DeMarco Murray celebrates a touchdown run during the second half of an NFL wildcard playoff football game against the Detroit Lions, Jan. 4, 2015, in Arlington, Texas.
AP / AP
Vanderbilt coach James Franklin celebrates with team as he dances on the sideline during the second half of the BBVA Compass Bowl NCAA college football game on Saturday, Jan. 4, 2014, in Birmingham, Ala. Vanderbilt defeated Houston 41-24. (AP Photo/Butch Dill)
NFL Commissioner Roger Goodell speaks at a press conference at the NFL's spring meeting in Atlanta on May 20, 2014.
Cal Sport Media / AP
Missouri defensive lineman Michael Sam (52) lets out a scream after sacking McNeese State quarterback Jacob Bower for a safety during the first half of the NCAA football game between the Mizzou Tigers and McNeese State Cowboys at the Edward Jones Dome in Columbia, Mo., Saturday, Sept. 11, 2010. Missouri defeated McNeese 50-6 (Cal Sport Media via AP Images)
AP / Cristobal Herrera
Former Miami Dolphins and NFL football star Chad Johnson appears with attorney Adam Swickle before Judge Kathleen McHugh during his court hearing, Monday, June 17, 2013, in Fort Lauderdale, Fla.
BRIAN SNYDER / REUTERS
Aaron Hernandez, former player for the NFL's New England Patriots football team, listens during a hearing at Attleboro District Court in Attleboro, Mass., August 22, 2013.
GARY HERSHORN / REUTERS
Beyonce performs during the half time show in the NFL Super Bowl XLVII football game in New Orleans, Louisiana, Feb. 3, 2013.
Carolyn Kaster/ AP
Washington Redskins football team owner Daniel Snyder arrives for the NFL fall meeting in Washington on Tuesday.
Elise Amendola / AP
The New England Patriots run onto the field before an NFL football game against the New York Jets Thursday, Sept. 12, 2013, in Foxborough, Mass.
Steven Senne / AP
New England Patriots tight end Aaron Hernandez before an NFL football versus the Houston Texans in Foxborough, Mass., on Dec. 10, 2012.
Morry Gash / AP
NFL football Super Bowl XLIII halftime performer Bruce Springsteen speaks at a news conference on Jan. 29
Bill Wippert / AP
Officials walk towards the field for an NFL football game between the Buffalo Bills and the Washington Redskins in Orchard Park, N.Y., Aug. 9, 2012
Patrick Semansky / AP
Ben Nix, from NFL security, carries the Vince Lombardi Trophy in preparation for a news conference between San Francisco 49ers head coach Jim Harbaugh and Baltimore Ravens head coach John Harbaugh for the NFL Super Bowl XLVII football game on Feb. 1, 2013, in New Orleans.
Mel Evans / AP
Lauren Silberman boots the ball during kicker tryouts at the NFL football regional combine workout Sunday, March 3, 2013, in Florham Park, N.J.
Dave Martin / AP
San Francisco 49ers' Colin Kaepernick warms up before the NFL football NFC Championship game against the Atlanta Falcons Sunday, Jan. 20, 2013, in Atlanta.
Matt Rourke / AP
Fans covered with snow wait in the stands before an NFL football game between the Philadelphia Eagles and the Detroit Lions, Dec. 8, 2013, in Philadelphia.
Tom Hauck / AP
The replacement referees talk during the game in an NFL preseason football game in Denver, Aug. 26, 2012.
Mike Segar / REUTERS
Former NFL football great and broadcaster Terry Bradshaw speaks during a presentation to announce Fox's new sports network "Fox Sports 1" in New York, March 5, 2013. Bradshaw will host a daily football program called "Fox Football Daily." Fox Sports 1 will begin broadcasting in August of 2013.
Elise Amendola / AP
Tim Tebow kneels in the end zone before an NFL divisional playoff football game against the New England Patriots Saturday, Jan. 14, 2012, in Foxborough, Mass.
Peter Morgan / AP
New York Giants' Peyton Hillis (44) rushes during the second half of an NFL football game against the Minnesota Vikings Monday, Oct. 21, 2013 in East Rutherford, N.J.
Bizuayehu Tesfaye / AP
In this Wednesday, July 24, 2013 file photo, former New England Patriots NFL football tight end Aaron Hernandez appears during a probable cause hearing at Attleboro District Court, in Attleboro, Mass.
Rick Wilking / Reuters
Denver Broncos quarterback Peyton Manning throws against the Philadelphia Eagles in the first quarter of their NFL football game in Denver September 29, 2013.
Matt Rourke / AP
Philadelphia Eagles' Nick Foles warms up as snow falls before an NFL football game against the Detroit Lions, Dec. 8, 2013, in Philadelphia.
Mel Evans / AP
New York Jets quarterback Geno Smith (7) throws a pass during the team's NFL football practice in Florham Park, N.J., Monday, Sept. 2, 2013.
Nick Wass / AP
Baltimore Ravens wide receiver Torrey Smith walks off the field after an NFL football game against the New England Patriots in Baltimore, Sunday, Sept. 23, 2012.
Jeff Wheeler / Minneapolis Star Tribune / MCT / Landov
Minnesota Vikings quarterback Brett Favre set an NFL record with his 271st consecutive start during a football game against the Lions in Detroit
Matt Slocum / AP
San Francisco 49ers head coach Jim Harbaugh reacts during the first half of the NFL Super Bowl XLVII football game against the Baltimore Ravens on Feb. 3, 2013, in New Orleans.
Elise Amendola / AP
NFL football commissioner Roger Goodell is surrounded by reporters after delivering a Dean's Distinguished Lecture at Harvard School of Public Health in Boston on Nov. 15, 2012, where he discussed some of the rules that have been created to limit concussions in the game of football.
Marcio Jose Sanchez / AP
San Francisco 49ers linebacker Aldon Smith (99) walks on the field during the fourth quarter of an NFL football game against the Indianapolis Colts in San Francisco, Sunday, Sept. 22, 2013.
John Froschauer / AP
Seattle Seahawks quarterback Russell Wilson makes a pass against the San Francisco 49ers in the first half of an NFL football game, Sunday, Sept. 15, 2013, in Seattle.
Pablo Martinez Monsivais / AP
In this Aug. 4, 2009, file photo, Washington Redskins helmets are displayed on the field during NFL football training camp at Redskins Park in Ashburn, Va.
Jonathan Bachman / Reuters
New Orleans Saints quarterback Drew Brees (9) smiles during an interview after winning their NFL football game in New Orleans, Louisiana October 7, 2012.
Ed Zurga / AP
Kansas City Chiefs fans cheer while setting a world record as the loudest stadium crowd during the second half of an NFL football game against the Oakland Raiders at Arrowhead Stadium in Kansas City, Mo., Sunday, Oct. 13, 2013.
Evan Vucci / AP
Dallas Cowboys quarterback Tony Romo looks for an opening to pass during the second half of an NFL football game against the Washington Redskins in Landover, Md., Sunday, Dec. 22, 2013.
David Goldman / AP
San Francisco 49ers punter Andy Lee looks on during a power outage in the second half of the NFL Super Bowl XLVII football game against the Baltimore Ravens in New Orleans, Feb. 3, 2013.
Matt Slocum / AP
Field judge Craig Wrolstad stands on the field after the lights went out during the second half of NFL Super Bowl XLVII football game in New Orleans, Feb. 3, 2013.
AP / AP
San Francisco 49ers punter Andy Lee (4) looks on during a power outage in the second half of the NFL Super Bowl XLVII football game against the Baltimore Ravens, Sunday, Feb. 3, 2013, in New Orleans. (AP Photo/David Goldman)
Mary Altaffer / AP
Dion Jordan, a defensive end from Oregon, stands with NFL Commissioner Roger Goodell after being selected third overall by the Miami Dolphins in the first round of the NFL football draft, April 25, 2013, at Radio City Music Hall in New York.
Wade Payne / AP
In this Dec. 17, 2012, file photo, then-New York Jets quarterback Tim Tebow warms up before an NFL football game in Nashville, Tenn. Tim Tebow is joining the New England Patriots, according to a report by ESPN on Monday, June 10, 2013.
Mike Groll / AP
New Orleans Saints quarterback Drew Brees holds the Vince Lombardi trophy after the NFL Super Bowl XLIV football game against the Indianapolis Colts in Miami, Sunday, Feb. 7, 2010
Nam Y. Huh / AP
Green Bay Packers quarterback Aaron Rodgers throws a pass against the Chicago Bears during the first half of an NFL football game, Dec. 29, 2013, in Chicago.
Tony Dejak / AP
Cleveland Browns tight end Kellen Winslow watches from the sidelines during an NFL football game against the Pittsburgh Steelers in Cleveland.
George Silk—Time & Life Pictures/Getty Images
Future Hall of Famer Andy Robustelli leads the Giants in a workout session at Yankee Stadium -- home to some of the greatest moments in NFL history, including the 1958 championship game between the Giants and the Baltimore Colts. (Ever-after known as "The Greatest Game Ever Played, the battle ended when the Colts won in sudden death overtime.) "Players today have contracts that pay them to train year-round," Grier says. "So they can concentrate on making themselves stronger and tougher and faster. In our day, we practiced to learn the plays and to keep our bodies in shape. But we weren't involved in weight-training and those kinds of things to make our bodies tough."
Indianapolis Colts quarterback Andrew Luck gets ready for an interview on the field after defeating the Detroit Lions during their NFL football game in Detroit, Michigan December 2, 2012.
Alex Brandon / AP
Detroit Lions tight end Joseph Fauria celebrates his touchdown reception with wide receiver Nate Burleson (13) during the first half of a NFL football game against the Washington Redskins in Landover, Md., Sunday, Sept. 22, 2013.
Green Bay Packers' Greg Jennings fails to catch a pass while playing against the Tampa Bay Buccaneers in the second half during their NFL football game in Green Bay, Wisconsin November 20, 2011. Jennings' surgery was postponed due to Hurricane Sandy
Elaine Thompson / AP
Seattle Seahawks' Cliff Avril, left, forces a fumble by San Francisco 49ers quarterback Colin Kaepernick in the first half of an NFL football game, Sunday, Sept. 15, 2013, in Seattle.
Stephen Brashear / AP
Officials signal a touchdown by Seattle Seahawks wide receiver Golden Tate, obscured, on the last play of an NFL football game against the Green Bay Packers, Sept. 24, 2012, in Seattle
In this Aug. 2, 2011, file photo, Chicago Bears wide receiver Sam Hurd watches teammates practice during NFL football training camp at Olivet Nazarene University in Bourbonnais, Ill.
New England Patriots' Julian Edelman (11) returns a fumble for a touchdown during the first half of an NFL football game against the New York Jets, Thursday, Nov. 22, 2012, in East Rutherford, N.J.
San Diego Chargers quarterback Philip Rivers (17) greets Denver Broncos quarterback Peyton Manning (L) after losing to Denver following their Monday Night NFL football game in San Diego, California October 15, 2012. The NFL is investigating the Chargers for possibly using banned "sticky substances."
LUCY NICHOLSON / REUTERS
Baltimore Ravens inside linebacker Ray Lewis holds up the Vince Lombardi Trophy after his team defeated the San Francisco 49ers in the NFL Super Bowl XLVII football game in New Orleans, Feb. 3, 2013.
AP / AP
Fans and members of the Baltimore Ravens and the San Francisco 49ers wait for power to return in the Superdome during an outage in the second half of the NFL Super Bowl XLVII football game, Sunday, Feb. 3, 2013, in New Orleans. (AP Photo/Gerald Herbert)
Tony Avelar / AP
San Francisco 49ers quarterback Colin Kaepernick (7) smiles on the sideline during the fourth quarter of an NFC divisional playoff NFL football game against the Green Bay Packers in San Francisco, Saturday, Jan. 12, 2013.
Jack Dempsey / AP
Denver Broncos kicker Matt Prater, left, celebrates a 64-yard field goal with Britton Colquitt during the first half of an NFL football game against the Tennessee Titans on Sunday, Dec. 8, 2013.
A police officer walks to an Independence, Mo., house house where police say Kansas City Chiefs linebacker Jovan Belcher fatally shot his girlfriend before driving to the NFL football team's training facility and shooting himself, Saturday, Dec. 1, 2012. (AP Photo/Charlie Riedel)
Tony Gutierrez / AP
Dallas Cowboys wide receiver Terrell Owens smiles as he stands on the sideline during a NFL pre-season football game against the Indianapolis Colts in Irving, Texas on Aug. 9, 2007.
Mike Segar / Reuters
New York Giants quarterback Eli Manning holds the Vince Lombardi Trophy after the Giants defeated the New England Patriots in the NFL Super Bowl XLVI football game in Indianapolis, Indiana, Feb. 5, 2012
David Goldman / AP
St. Louis Rams running back Daryl Richardson (26) is hit by Atlanta Falcons outside linebacker Sean Weatherspoon (56) during the first half of an NFL football game, Sunday, Sept. 15, 2013, in Atlanta.
Chris Keane / Icon SMI / Corbis
Arizona Cardinals quarterback Kurt Warner celebrates his team's win against the Carolina Panthers in their NFC Divisional Round NFL playoff football game in Charlotte, North Carolina, January 10, 2009.
Denis Poroy / AP
Denver Broncos quarterback Peyton Manning fumbles as he is hit by San Diego Chargers outside linebacker Tourek Williams during the third quarter of a NFL football game Sunday, Nov. 10, 2013, in San Diego.
Indianapolis Colts quarterback Andrew Luck celebrates as he runs off the field after their 30-27 win over the Green Bay Packers in an NFL football game in Indianapolis, Sunday, Oct. 7, 2012.
David J. Phillip / AP
New Orleans Saints kicker Garrett Hartley celebrates after kicking the game winning field goal during overtime in the NFC Championship NFL football game in New Orleans on Jan. 24, 2010
Patrick Semansky / AP
Washington Redskins quarterback Kirk Cousins spikes the ball after a two point conversion to tie the game and force overtime during the second half of an NFL football game against the Baltimore Ravens in Landover, Md., Sunday, Dec. 9, 2012.
Michael Conroy / ASSOCIATED PRESS
Indianapolis Colts quarterback Andrew Luck (12) dives for a touchdown after recovering a fumble by the Colts' Eric Berry during the second half of an NFL wild-card playoff football game against the Kansas City Chiefs Saturday, Jan. 4, 2014, in Indianapolis.
Marty Lederhandler / AP
In this Nov. 11, 1970, file photo, Pat Summerall, former New York Giants place kicker and now CBS sportscaster, discusses the field goal explosion in NFL football in New York.
Brian Snyder / Reuters
New York Jets place kicker Jay Feely (3) kicks an overtime, game-winning field goal against the New England Patriots in their NFL football game in Foxborough, Massachusetts November 13, 2008.
Alex Brandon / ASSOCIATED PRESS
FILE - In this Saturday, Aug. 4, 2012 file photo, Zena "Chief Z" Williams, unofficial mascot of the Washington Redskins, signs autographs during fan appreciation day at the Redskins' NFL football training camp at Redskins Park in Ashburn, Va.
Bill Haber – AP
Washington Redskins quarterback Robert Griffin III (10) throws a touchdown pass under pressure from New Orleans Saints free safety Malcolm Jenkins (27) in the first quarter of an NFL football game at Mercedes-Benz Superdome in New Orleans, Sunday, Sept. 9, 2012.
Don Wright / AP
Chicago Bears running back Matt Forte (22), steps out of bounds after getting hit by Pittsburgh Steelers strong safety Troy Polamalu (43) on a long run in the first quarter of an NFL football game on Sunday, Sept. 22, 2013, in Pittsburgh
Nick Wass / AP
Baltimore Ravens head coach John Harbaugh, left, chats with his brother, San Francisco 49ers head coach Jim Harbaugh, center, and their father, Jack, before their NFL football game in Baltimore on Thursday, Nov. 24, 2011.
(L-R) New England Patriots kicker Stephen Gostkowski lays on the ground after missing a field goal as Patriots punter Zoltan Mesko reacts while Arizona Cardinals players Justin Bethel, Adrian Wilson, and Patrick Peterson celebrate their win during the final second of the fourth quarter of their NFL football game in Foxborough, Massachusetts September 16, 2012.
Northwestern football players gesture during practice at the University of Wisconsin-Parkside campus on Aug. 17, 2015, in Kenosha, Wi.
Jesse Grant—Getty Images
Suge Knight arrives at the NFL Draft Inauguration Party hosted by Desean Jackson and Fred Davis at Sugar nightclub on April 29, 2008 in Hollywood.
Former NFL All-Pro safety Darren Sharper looks toward his attorney, Blair Berk, during an appearance in the Los Angeles Superior Court on Feb. 20, 2014.
Seattle Seahawks head coach Pete Carroll looks towards the referee for a call in the first quarter against the New England Patriots during the NFL Super Bowl XLIX football game in Glendale, Ariz. on Feb. 1, 2015.
Mark Cunningha — Getty Images
A detailed view of an NFL shield logo painted on the field before the game between the Detroit Lions and the Tampa Bay Buccaneers at Ford Field on Nov. 24, 2013.
New Jersey Gov. Chris Christie, left, and Dallas Cowboys owner Jerry Jones talk before an NFL football game between the New York Giants and the Cowboys on Sept. 8, 2013, in Arlington, Texas.
Houston Texans' J.J. Watt poses for a selfie with St. Louis Rams' Robert Quinn after Team Irvin defeated Team Carter 32-28 in the NFL Football Pro Bowl on Jan. 25, 2015
Bob Levey—Getty Images
NFL running back Adrian Peterson of the Minnesota Vikings addresses the media after pleading "no contest" to a lesser misdemeanor charge of reckless assault on Nov. 4, 2014 in Conroe, Texas.
Jamie Sabau—Getty Images
NFL Commissioner Roger Goodell meets fans on the field before a game between the New York Jets and Buffalo Bills at Ford Field on November 24, 2014 in Detroit, Michigan.
Leon Halip—Getty Images
NFL Commissioner Roger Goodell attends the Buffalo Bills-New York Jets game at Ford Field on November 24, 2014 in Detroit, Michigan.
Seattle Seahawks middle linebacker Bobby Wagner (54) gets past New England Patriots running back Brandon Bolden (38) after intercepting a pass during the second half of NFL Super Bowl XLIX football game Sunday, Feb. 1, 2015, in Glendale, Ariz.
Gene J. Puskar—AP
NFL football Hall of Fame quarterback Dan Marino at a baseball game between the Pittsburgh Pirates and the Milwaukee Brewers in Pittsburgh on Aug. 29, 2013.
Michael Zagaris—Getty Images
NFL Commissioner Roger Goodell sits in the crowd during the the Ribbon Cutting Ceremony for Levi Stadium on July 17, 2014 in Santa Clara, California.
Kyle Terada—USA Today Sports
NFL commissioner Roger Goodell walks the sidelines before the game between the Seattle Seahawks and the Green Bay Packers at CenturyLink Field on Sept. 4, 2014 in Seattle.
Doug Pensinger—Getty Images
The NFL logo is displayed on the turf as the Denver Broncos defeated the Kansas City Chiefs 24-17 at Sports Authority Field at Mile High on September 14, 2014 in Denver, Colorado.
Minnesota Vikings running back Adrian Peterson warms up for an NFL football game in St. Louis on Sept. 7, 2014
Suspended Minnesota Vikings running back Adrian Peterson exits following his hearing against the NFL over his punishment for child abuse, in New York Dec. 2, 2014