A regulation basketball used in NBA play is inflated to an air pressure between 7.5 and 8.5 pounds of pressure per square inch. Many balls are inflated to the average pressure of 8 pounds.
Regulating a basketball's air pressure ensures fair playing conditions throughout a league. A ball's internal air pressure determines the height of its bounce. Using Newton's laws of motion as an explanation, the ball's internal pressure applies force to any surface it hits, causing an equal force to repel it in the opposite direction. A player can't effectively dribble an underinflated ball because the ball lacks sufficient force to bounce back to its original height. An overinflated ball has a very high internal pressure and would bounce too high for a player to easily control its direction.