9.5 Obstruction 9.5.1 Obstruction occurs when: 9.5.1.1 A defensive player, neither in possession of the ball nor in the act of fielding a batted ball, impedes a batter’s attempt to make contact with a pitch or impedes the progress of any runner who is legally running bases on a live ball. It can be intentional or unintentional. 9.5.1.2 A defensive player, while not in possession of the ball: a. Blocks any part of the leading edge of first, second or third base or home plate (as defined); or b. Otherwise blocks the runner from advancing or returning to a base. 9.5.2 The defensive player is not considered obstructing if they are in possession of the ball or they are, in the judgment of the umpire, making a legitimate reaction to the trajectory of the ball after it is thrown.
Notes: 1. Once in possession of the ball, the defensive player can be positioned between the runner and the base/plate. 2. Obstruction may be ruled even though there is no physical contact. 3. If in the umpire's judgment, the runner would have clearly been put out then the obstruction is ignored. 4. Obstruction can occur on a force or tag play.