In baseball, there are several occurrences which are called interference. 

Contents

1 Offensive interference 1.1 Cases 2 Umpire's interference 3 Catcher's interference 4 Fan interference 4.1 Infamous cases of possible fan interference 5 Weak interference 6 Common misconceptions

Offensive interference

Most commonly, it is interference when a member of the offensive team physically hinders the defensive team, decreasing their chances to make an out or increasing the chance that a baserunner will advance. Whenever this offensive interference occurs, the ball becomes dead. If the interference was committed by a batter or a baserunner, that player is out and all other runners return to the bases they occupied at the time of the interference. If interference is committed by a runner with the possible intent of preventing a double play, the batter-runner will be called out in addition to the runner who committed the interference. If interference is committed by the batter-runner before he reaches first base with the possible intent of preventing a double play, the runner closest to scoring will be called out in addition to the batter-runner. If interference is committed by a retired runner or by some other member of the offensive team, the runner who is most likely to have been put out will be called out.

Under high school (NFHS) rules only, if interference is committed by a runner with the effect of preventing a likely double play, regardless of his intent, the batter-runner will be called out in addition to the runner who committed the interference.

In addition to the general subjective definition of offensive interference, it is also interference by specific rule when:

• The bat hits the ball a second time in fair territory, such as while the bat is being dropped;
• A batter or runner intentionally deflects the course of a batted ball in any manner;
• A member of the offense team stands near a base to impersonate a baserunner or to otherwise confuse or hinder the defense;
• A coach physically assists a runner in returning to or leaving first or third base;
• A batter is struck by a ball thrown from the home plate area while running to first base with a foot entirely outside the three-foot running lane, before the batter reaches first base;
• A runner makes contact with a batted ball which did not go through or by a fielder, unless no infielder had a chance to immediately field the ball;
• A runner makes contact with a fielder attempting to field a batted ball, except the batter with a catcher in the immediate vicinity of home plate immediately after the ball was batted; or
• A member of the offensive team intentionally touches a thrown ball, or intentionally hinders a fielder attempting to make a throw

There are some exceptions to the penalty for offensive interference.

• If there are fewer than two outs and a runner is trying to score, but the batter commits interference with the tag attempt at home plate, then the runner is out for the batter's interference; the batter is not out. If there are two outs in this situation, the normal interference penalty applies; the batter is out and the run does not score.

Cases

On Tuesday, October 19 2004, in game six of the 2004 American League Championship Series, Alex Rodriguez of the New York Yankees intentionally swatted the arm of Boston Red Sox pitcher Bronson Arroyo, who was attempting to tag Rodriguez out. The ball came loose, initially enabling Rodriguez to advance and the previous runner Derek Jeter to score, but instead Rodriguez was ruled out on the interference, under the general definition of the rule above. The Red Sox went on to win the game and the series.

Umpire's interference

It is umpire's interference when the umpire inadvertently hinders a catcher's throw after he catches a pitch. In this case, the ball is dead and the runners must return to their time of pitch base.

It is also umpire's interference when an umpire is struck by a fair batted ball before it touches or passes an infielder other than the pitcher. This can occur because umpires often position themselves inside the diamond. In this case, the ball is dead, the batter-runner is awarded first base, and all other runners advance only if forced.

Catcher's interference

It is catcher's interference when the catcher physically hinders the batter's opportunity to legally swing at a pitched ball. In this case, play continues, and after continuous playing action ceases, the umpire will call time. The penalty here is that the batter is awarded first base, any runner attempting to steal is awarded that base, and all other runners advance only if forced. If the actual playing result is more advantageous than the penalty, the offense may elect to ignore the infraction. If the batter-runner reaches first safely and all other runners advance at least one base, catcher's interference is ignored by rule.

Under high school (NFHS) rules only, catcher's interference is instead called catcher's obstruction. Catcher's interference occurs most often when a catcher squats too close to home plate, so that the batter's bat touches the catcher's glove as the batter swings.

Fan interference

When a fan or any person not associated with one of the teams alters play in progress, it is fan interference. The ball becomes dead, and the umpire will award any bases or charge any outs that, in his judgment, would have occurred without the interference.

Fan interference often occurs when a fan in the first row of seats reaches over the field to attempt to grab a fair or foul fly ball. If the umpire judges that the fielder could have caught the ball over the field, he will rule the batter out on fan interference.

Umpires typically clasp their hands together over their head as a signal when fan interference occurs.

Infamous cases of possible fan interference

On October 9, 1996, Jeffrey Maier became well-loved in New York but hated in Baltimore over a possible fan interference that was not called by the umpire, thus resulting in a game-tying home run for the New York Yankees in the American League Championship Series.  The Baltimore Orioles went on to lose the game and the series.

On October 14, 2003, Cubs fan Steve Bartman was villified for his role in preventing Chicago Cubs fielder Moises Alou from catching a foul fly ball in Game 6 of the National League Championship Series; in this case, no fan interference was possible because the fly ball was not over the field, but over the seats. Bartman later stated that he was caught up in the excitment of the moment and didn't even think that the ball might be catchable by Alou. The out-cum-foul ball gave the Cubs opponents, the Florida Marlins, the opportunity to gain eight runs in the inning. Thus the Marlins took the lead, won the game, and then went on to win the series.

Weak interference

Several situations arise in baseball that are considered, by logical extension of the rules, as weak interference. These well-defined incidents are not severe enough to be considered offensive interference. When weak interference occurrs, the ball is usually called dead, but no further penalty is assessed against a baserunner or batter.

Weak interference is called is called when:

• A catcher touches the batter or his bat before a pitch; or
• A foreign object or animal flies between home plate and the pitcher before or during a pitch
• A non-participant or member of the offensive team grasps a live ball, but no play is affected and no runners attempt to advance

Common misconceptions

When a fielder hinders a baserunner, the situation is called obstruction, not interference. Baseball commentators will often mistakenly refer to obstruction as interference.

Not all physical contact in baseball is interference. Some accidental contact which has no or very little effect on play will usually be ignored; physical contact must result in an advantageous situation for the offense to be considered offensive interference.

A base does not provide a runner immunity from an offensive interference call; a runner is required to avoid a batted ball or a fielder going after a batted ball, even if it means vacating a base where he wishes to remain. The only exception is that a runner is not held liable if an infield fly touches him as he tries to avoid it yet remain on a base.

For the most part, intent to interfere is not necessary for interference to be called; however, a runner can not be called for interference with a throw or a fielder making a throw unless such a hinderance was indeed intentional.