Atlanta Hawks Fan Injured During In-Game Challenge, Stretchered Off Court

12:21 PM PT -- The Hawks gave an update on the fan to TMZ Sports on Wednesday ... saying, "We have reached out to the season ticket member injured last night while participating in an on-court game during a timeout."

"He is in good spirits and expects a full recovery."

An ATL fan appeared to suffer an ACL injury on Tuesday night ... going down with what seemed like a bad knee ailment during a challenge at the Hawks game.

The painful scene took place amid an intermission at the Hawks vs. Trail Blazers tilt at State Farm Arena ... when an Atlanta-backer was picked to participate in a basketball version of Tic-Tac-Toe.

The guy -- wearing a Hawks sweatshirt -- was supposed to hit a few layups before his opponent ... and score a Tic-Tac-Toe win in the process.

The problem? As he went up for his first bucket, his knee gave out ... and he crumpled to the floor in pain.

The game actually had to be put on pause so medics could tend to the man. Eventually, he was stretchered off the floor ... as some of the NBA players nearby watched in disbelief.