Obstruction is an act by which the defensive team impedes the batting team from advancing around the bases.
Section 2:00 of the Official Rules describes obstruction as follows:
- OBSTRUCTION is the act of a fielder who, while not in possession of the ball and not in the act of fielding the ball, impedes the progress of any runner.
- Rule 2.00 (Obstruction) Comment: If a fielder is about to receive a thrown ball and if the ball is in flight directly toward and near enough to the fielder so he must occupy his position to receive the ball he may be considered "in the act of fielding a ball." It is entirely up to the judgment of the umpire as to whether a fielder is in the act of fielding a ball. After a fielder has made an attempt to field a ball and missed, he can no longer be in the "act of fielding" the ball. For example: If an infielder dives at a ground ball and the ball passes him and he continues to lie on the ground and delays the progress of the runner, he very likely has obstructed the runner.
Obstruction is also explained in detail in Section 7.06 of the rules, which deals with the runner:
- When obstruction occurs, the umpire shall call or signal "Obstruction."
- If a play is being made on the obstructed runner, or if the batter-runner is obstructed before he touches first base, the ball is dead and all runners shall advance, without liability to be put out, to the bases they would have reached, in the umpire's judgment, if there had been no obstruction. The obstructed runner shall be awarded at least one base beyond the base he had last legally touched before the obstruction. Any preceding runners, forced to advance by the award of bases as the penalty for obstruction, shall advance without liability to be put out.
- Rule 7.06(a) Comment: When a play is being made on an obstructed runner, the umpire shall signal obstruction in the same manner that he calls "Time," with both hands overhead. The ball is immediately dead when this signal is given; however, should a thrown ball be in flight before the obstruction is called by the umpire, the runners are to be awarded such bases on wild throws as they would have been awarded had not obstruction occurred. On a play where a runner was trapped between second and third and obstructed by the third baseman going into third base while the throw is in flight from the shortstop, if such throw goes into the dugout the obstructed runner is to be awarded home base. Any other runners on base in this situation would also be awarded two bases from the base they last legally touched before obstruction was called.
- (b) If no play is being made on the obstructed runner, the play shall proceed until no further action is possible. The umpire shall then call "Time" and impose such penalties, if any, as in his judgment will nullify the act of obstruction.
- Rule 7.06(b) Comment: Under 7.06(b) when the ball is not dead on obstruction and an obstructed runner advances beyond the base which, in the umpire's judgment, he would have been awarded because of being obstructed, he does so at his own peril and may be tagged out. This is a judgment call.
- NOTE: The catcher, without the ball in his possession, has no right to block the pathway of the runner attempting to score. The base line belongs to the runner and the catcher should be there only when he is fielding a ball or when he already has the ball in his hand.
When obstruction is called, the umpire will award the baserunners as many bases as they would have earned, in his judgment, if the obstruction had not occured. The play may be allowed to continue, with any additional bases being awarded after the action has stopped. The fielder guilty of obstruction is charged with an error.
A similar act by the batting team is called interference. There is often a fine line between interference and obstruction in the case of a ball hit along the first base line, for example, as the fielder is entitled to field the ball unimpeded, while the batter-runner is entitled to run directly to first base. If a collision does occur at that point, the umpire must exercise his judgment to determine which player is at fault.