A quarterback for the New York Jets won't be able to play for at least six weeks after a team-mate "sucker-punched" him and broke his jaw.
Geno Smith and linebacker Ikemefuna Enemkpali got into an altercation inside the locker room.
Jets Coach Todd Bowles said "It had nothing to do with football, it was something very childish."
Enemkpali, a relative newcomer, lost his job after landing the punch.
"You don't walk up to another man and punch him in the face," Bowles said.
The team was training for the upcoming NFL American football season, which begins later this month. Smith is expected to miss several games.
Smith, who was competing to become the team's starting quarterback, will need surgery to fix his jaw.
With Smith sidelined, the team's other quarterback Ryan Fitzpatrick is likely to assume the starting role.
Later Smith posted a closed-mouthed photo on Instagram with the caption "I'll be back".
Enemkpali was a sixth-round draft pick by the Jets in 2014 and played only 40 snaps as a rookie. He was suspended in 2011 while attending Louisiana Tech following an arrest for punching an off-duty police officer.
The Jets went 4 and 12 last season.