The purpose of the present study was to investigate when a baseball batter decides to hit the ball and how he adjusts the bat movement to hit it effectively. Six collegiate baseball players were requested to hit the ball that was hung and remained still by a thread connected to an electric magnet. The ball could be dropped by the gravity when the electric circuit was switched off (OFF). They were allowed to stop the motion if they judged it to be ‘ball’ because of ball drop. Batting motion was videotaped by means of a high-speed video camera (250 frames/s), and the bat head position at the moment of ball-bat contact (BBC) was recorded.

Batting motion could be stopped when the ball was dropped more than 0.1 s before the front foot contact on the ground (FFC) . When dropped 0~0.1 s after FFC, the bat passed above the ball but the bat head position at BBC was modified. According to the regression analysis between the bat head position at BBC and the time of OFF, baseball batters were considered to decide the bat movement by watching the ball position 0.042~0.184 s after FFC (0.077~0.154 s before BBC). These results suggested a highly trained batter could modify the bat trajectory after he had decided to hit.