Four years ago this week, star linebacker Junior Seau retired from the New England Patriots, ending a storied NFL career that included a dozen Pro Bowls and the myriad accolades afforded a once-in-a-generation player. Much has happened since. Today, the last team that Seau played for—the perennially dominant Patriots—will square off against the Denver Broncos for a chance to play in Super Bowl XLVIII. Meanwhile, Seau, who suffered brain trauma after decades of playing football and committed suicide in 2012, would have celebrated his 45th birthday today.

In the years since Seau's retirement, the issue of head injuries in the NFL has slowly crept into the public consciousness. The link between the sport’s signature brutal hits and their deleterious aftermath is now part of a debate taking place both on and off the field. As we noted earlier this week, a district judge rejected an initial settlement over a concussion lawsuit brought against the NFL by a number of former players. The judge’s rationale for rejecting the $765 million settlement was that she feared “the sum may not be enough to cover injured players." 

On the field, this year’s NFL postseason has been marred by a slew of head injuries. Nine different players suffered concussions in the first five playoff games, including three members of the Kansas City Chiefs in one game. David Bakhtiari and Keenan Lewis, two of those nine players, refused to leave the sideline and were later cited by the league for violating concussion protocol during playoff games, a violation that carries no consequence for the players or their teams.

Despite not being cleared to play by doctors, Bakhtiari returned to the field. Lewis was seen on camera pleading with his coaches to let him return, which led NBC analyst Cris Collinsworth to remark on how far he felt the league had come: “When I was playing football, he would be back in the game. The doctors now are taking a much stronger approach to this issue.”

Between rule changes and new concussion protocols, one could argue that the league has made an effort to limit what is ultimately an ineradicable problem with the sport. When Seattle and San Francisco do battle in the NFC Championship tonight, the Seahawks will be without their star wide receiver Percy Harvin, who had to be helped off the field during last week’s game against the New Orleans Saints on two separate occasions after suffering injuries to the head. According to his coach Pete Carroll, Harvin "wants to play," but is being held out because he wasn't able to complete the NFL's concussion safety protocol in time.

This brings us back to Seau, who once boasted in a 1993 NFL Films video that "If I can feel some dizziness, I know that guy is feeling double." Like several other players before him, Seau was said to have experienced mood swings as well as "signs of irrationality, forgetfulness, insomnia and depression" late in his life. After his death in 2012, Seau's family sent his brain to the National Institute of Neurological Disorders and Stroke for examination. (Like former player Dave Duerson, Seau took his own life by shooting himself in the chest.)

Last year, the family released the findings, which revealed that Seau had been suffering from Chronic Traumatic Encephalopathy (CTE), a degenerative disease brought on by head injuries. It was a condition that Seau had shared with a number of former players. Two weeks later, the family brought a wrongful death lawsuit against the NFL, accusing the league of obscuring the long-term effects of repeated hits to the head. More than 4,800 former players have also sued the league. While the legal wrangling between the league and its former players continues to play out in the courts, the games, as always, go on.