Scary moment for Shareef O'Neal ... who appeared to be seriously injured during a high school basketball game Monday night when he went up for a shot and came down on his head.
Shaq's son was making his senior season debut for Crossroads High School in a game against Beverly Hills High and was lighting it up with 31 points ... until the injury.
Shareef went up in traffic for a layup but his legs got tangled with the defenders -- and he came crashing down hard without bracing himself. You can hear the crack on the court -- and Shareef was holding his head in pain afterward.