A player stands about 10 feet from a wall, facing the wall. A coach or another player throws a ball high off the wall so it caroms to one side of the player, shoulder height or higher. The player quickly reacts and moves to the ball. practice both two hand catches and block and tuck catches. Alternative: Throw the ball off the backboard at an angle. Also, use two tennis balls - throw and react.

SEE - REACTION REBOUNDING BASKETBALL HQ https://youtu.be/vnD4OSptaEk