It’s no secret that football is a violent sport that can result in some serious injuries, but four National Football League (NFL) teams may have crossed a legal line by putting secret bounties on opposing players, including quarterbacks Brett Favre and Kurt Warner.

The Washington Redskins, Buffalo Bills, Tennessee Titans and New Orleans Saints were allegedly involved in “pay for pain” programs that financially rewarded defensive players for inflicting game-ending hits on opponents. Knockouts were worth $1,500, and cart-offs netted $1,000. Defensive coordinator Gregg Williams, who left the Saints for the Saint Louis Rams in the off-season, coached all four teams.

The NFL likely will hand down punishments that could include loss of draft picks, fines and suspensions, but the teams also may face legal action from injured opponents. The central question is whether players accept the possibility of injury simply by playing, or whether the bounty system represented a risk beyond normal expectations.

Football hits have been criminally prosecuted in the past. In 1973, Cincinnati Bengals fullback Boobie Clark struck Denver Broncos defensive back Dale Hackbart on the back of the neck with his forearm after an interception. Although he played for several more weeks, Hackbart was eventually diagnosed with a career-ending neck fracture. He filed a $1 million lawsuit against Clark. An appeals court ruled that players can be held responsible for recklessly endangering opponents.

The teams also could face a class action civil suit from fans who attended the games in question, according to Reuters. If fans claim that they paid to watch games based on athletic skill, not secret bets, they could potentially recover ticket costs.