Out of bounds and possession explained
When the ball is out of bounds in basketball, why touching the line counts as out, how possession is decided, and what happens on a shared touch.
When the ball is out
In basketball the boundary lines are treated as being out of bounds, not part of the playing area. The ball is out of bounds when it touches the floor or any object on or outside the boundary line, or when it touches a player who is out of bounds. Unlike some sports where the whole ball must cross the line, here even touching the line itself counts as out, so the boundary is unforgiving.
The player counts too
A player is out of bounds when any part of their body touches the floor on or outside the boundary line. This is why players fighting to save a ball reach and jump from inside the line, releasing it back into play before their feet come down out of bounds. If a player holding or touching the ball is standing on or over the line, the ball is out, regardless of where the ball itself is in the air.
Who gets the ball
When the ball goes out of bounds, possession is awarded to the team that did not cause it to go out, meaning the opponents of whoever touched it last. That team then restarts play with a throw-in from the sideline or baseline near where the ball went out. This simple last-touch rule decides possession on the great majority of out-of-bounds plays, which is why players are so careful about who makes final contact.
When it is unclear
Sometimes two opposing players touch the ball at virtually the same moment as it goes out, and officials cannot tell who touched it last. In that case the ball is not simply given to one side by guesswork; a set procedure decides possession, and at higher levels officials may use replay to determine the last touch. These shared-touch situations are among the trickiest calls in deciding out-of-bounds possession.