What causes the ball to turn white and lose momentum in Ghost Hunt mode?

In ghost hunt, if the ball is untouched, it will hover in place a few feet off the ground. When a player hits the ball, the ball changes to the color of that player's team and will move with normal ball physics until it hits the ground again. Upon hitting the ground, it turns white and slows to a stop, returning to its idle hovering state. If the ball was hit in such a way that it is rolling on the ground, it will turn white after a second or two of rolling and return to its hovering state.

If the ball is caught in a player's beam, then the ball will follow the player and the above rules don't apply.