The worst fear for the missing Ohio State football player Kosta Karageorge was confirmed Sunday when he was found dead from an apparent self-inflicted gunshot wound. He had been missing since Wednesday.

Karageorge was a walk-on this year after spending the previous three years on Ohio State’s wrestling team. He had one tackle in his only game played this season. Despite the limited playing time on the football field, Karageorge had a history of concussions.

Multiple reports state Karageorge sent a few texts before disappearing Wednesday morning. One was to his mother, in which he apologized for being “an embarrassment.” In another text to his old wrestling coach, Karageorge said he loved him, according to the New York Times. These were unusual behaviors for Karageorge. His sister told the Times Karageorge suffered confusion, became disoriented and had frequent mood swings due to concussions.

Whether or not these symptoms came as a direct result of concussions, Karageorge is not the first person in sports to experience behavioral changes after suffering a concussion, let alone commit suicide. In fact, he’s added to a list that’s becoming longer at an alarming rate.

Since 2011, there have been a number of high-profile athletes who have died due to symptoms directly related to concussions.

The first was Derek Boogaard, a hockey enforcer who died in May 2011 due to a drug overdose. He became addicted to pain killers after chronic headaches and body aches from numerous fights in the NHL. Later that summer, two more hockey players, Wade Belak and Rick Rypien, committed suicide due to depression. Depression has become a well-known outcome because of repeated concussions.

In 2012, the football world was rocked when 12-time Pro Bowler Junior Seau shot and killed himself. And later that year, Jevon Belcher shot his girlfriend before killing himself at the Kansas City Chiefs practice facility.

All five of these players, along with numerous others, have been diagnosed with CTE, a degenerative brain disease caused by repetitive hits to the head. It is unknown whether Karageorge will be diagnosed with the same disease, as it only can be discovered after death by looking at the brain. Regardless of whether or not he had CTE, sports, especially those as violent as hockey and football, need to actively reduce head trauma.

The NHL has done this through Rule 54, which makes it illegal to target the head for a hit or deliver a blind-side hit. Football has instituted rules to make any hit to the head illegal, as well as protecting defenseless players, especially the quarterback, wide receiver and kicker. However, these rules are not enough.

Both leagues need to change the culture surrounding the hits and the players. Yes, fans love big hits. However, nothing will change until the players respect their opponents and are educated on the dangers of hits to the head. The leagues must acknowledge that helmets only prevent less damage rather than any damage, and must make sure hits are to the body rather than the head. And knowing what happens when you hit someone in the head will start to change the mentality of players.

It should not take another tragedy like Karageorge’s to force leagues to make changes to protect their players. And while leagues are making the right strides, much more work needs to be done to prevent any more tragedies.