"Riding the Board" is a term in diving that describes the action of landing on the board during a hurdle as the board is moving down, toward the water instead of up and away from the water. The timing during the hurdle allows the diver to gain the most spring from the board.
If the lands on the board on its downward path, the board will then naturally rebound up and the diver will gain lift. If the diver lands on the board while it is moving up and away from the board, the diver will stop the board from moving - the diver and the board will be moving in opposite directions, and the amount of spring will be decreased.
In a forward approach in diving, a goal of every diver is to work in concert with the diving board to get the most amount of height - known as "riding the board."

