This play happens quick and you need to know where the offensive player was last in contact with the floor. Following the missed layup, the offensive player's momentum takes him OOB. This is legal and should NOT be penalized as leaving the floor for an unauthorized reason. However, when the ball is coming toward him, he jumps in the air after last being in contact with the floor out of bounds. When the ball contacts him before he makes contact with the floor inbounds and is no longer touching OOB a violation has occurred.