A phrase that describes the act of rebounding the ball in basketball. It is used because the back of the hoop structure is called a "backboard", and the ball often bounces off the backboard before being rebounded by a player. The verb "crash" is used because it is optimal basketball strategy if players move quickly to rebound the ball. This often requires physical contact with other players on the court, which is why players must "crash" the boards. Coaches often insist that players "attack" the boards as well.
The act of crashing the boards is just as important as boxing out. In fact, they go hand in hand, as a "crasher" is often sought out by the opposition as a primary target for boxing out. Rebounding is one of the most important skills in basketball outside of shooting. The famous basketball coach Red Auerbach always approached building his teams with rebounding in mind, and he won many NBA championships across decades with players like Hall of Fame rebounders Bill Russell and Larry Bird.