The Pro Hitter is a batting aid used by more than half the hitters in the Major Leagues. It helps keep a firm grip on the bat at contact for more solid contact and increased performance.
The Pro Hitter fits on the top thumb when batting with the rounded side in the web between the thumb and index finger.
Proper bat grip dictates the bat being held in the fingers rather than the palm of the hands. At contact, the bat moves back into the webbing of the top hand between the thumb and index finger causing a loss of solid connection between the hands and bat. The Pro Hitter serves to maintain a solid grip on the bat at contact which means more power and harder hits.