Reverse Forearm Bounce
The term was originally coined by Dr. Mike Marshall as "reverse pitching forearm bounce."
Dr. Marshall identifies the "bounce" as the downward motion of the pitching forearm caused by the inertial mass of the ball, pitching hand, and pitching forearm.
For many pitchers with traditional deliveries, this arm action is what turns the forearm over. Because the turnover occurs after the acceleration phase has started, this is called late forearm turnover.
Reverse forearm bounce does not occur in all pitchers, but it is more violent in pitchers with certain mechanical elements. For example, when a pitcher forcibly delays ball pick-up or powerfully externally rotates his arm, he dramatically increases his chances of experiencing reverse forearm bounce.