Some good explanation of intereference and obstruction

http://baseball-rules.com/umphelp.htm

I believe interference is the toughest call an umpire has to make. It is a call based solely on the umpire's judgment. To make a good judgment as to whether or not interference occurred, the umpire must understand the definition as stated in the rules so it can be recognized when it occurs. After interference is called, the proper rule must be applied.

The definition as stated in Rule 2.00 is:

"(a) Offensive interference is an act by the team at bat which interferes with, obstructs, impedes, hinders or confuses any fielder attempting to make a play. If the umpire declares the batter, batter-runner, or a runner out for interference, all other runners shall return to the last base that was in the judgment of the umpire, legally touched at the time of the interference, unless otherwise provided by these rules.

It should be noted that (b) above is the only defensive interference. Hindering the runner by the defense is OBSTRUCTION.

How do we interpret this rule? The key, is to focus on the phrase "interferes with, obstructs, impedes, hinders or confuses." Those words cover a lot of actions. The umpire, after witnessing an act by the offense must ask himself the following question; "Did the offense interfere with, obstruct, impede, hinder or confuse the fielder attempting to make the play?" If the answer is yes, interference should be called. The call must be made as soon as possible. When interference is called the ball is immediately dead and no runners may advance beyond the base they held at the time of the interference. The umpire must be aware of where all runners are at the time of the call.

Some interference calls are easy.
Example: If a runner is hit by a batted ball he is out and no judgment of intent is required unless he is hit by a deflected ball, or the ball has passed on infielder, in which case the umpire must decide if he intended to be hit to interfere, obstruct, impede, hinder or confuse the defense or if another fielder had a play on the ball. Rule 5.09(f) and 7.08(f).
Example: A runner must avoid a fielder attempting to field a BATTED BALL. If he does not he is guilty. This is a fairly easy call. Rule 7.09(L) and 7.08(b).

The fielder's protection begins the moment the ball is hit. That protection continues as he completes his initial play. His protection ends if he misplays the batted ball and has to move to recover it. Contact with the fielder is not necessary for interference to be called.

Difficult calls are the ones involving thrown balls. Interference with a thrown ball must be judged as an intentional act. Rule 7.08(b), 7.09(L). If a runner is hit by a thrown ball while running the bases, he is not out unless the umpire judges that the runner intentionally interfered, obstructed, hindered or confused the defense attempting to make a play.

Some examples of interference are:

• Yelling at a fielder as he attempts a catch or play (Note that the rule states "the team at bat.." This includes coaches and players on the bench.
• Waving his arms to distract the fielder
• Making contact with the fielder as he attempts a throw
• Making contact with the fielder as he attempts to catch a batted ball
• Making INTENTIONAL contact with a fielder as he attempts to catch a thrown ball. The runner has a right to the base path except when a fielder is attempting to field a BATTED ball
• Making INTENTIONAL contact with a thrown ball
• Stopping directly in front of a fielder attempting to field a ground ball

COLLISIONS VS INTERFERENCE

The runner has a right to an unobstructed path while running the bases. The fielder has a right to make a play without interference. The runner has the right to the base path except when a fielder is attempting to field a BATTED BALL or has possession of the ball.

Sometimes when the runner and fielder collide, no penalty should be applied. The umpire must judge whether someone's rights were violated. This applies mainly to plays where the throw and the runner are arriving at the same time. There is no such thing as a must slide rule. When a runner collides with a fielder attempting to field a batted ball, he should be called out in almost all cases. If the runner collides with a fielder attempting to catch a throw, the umpire must first decide if the collision was intentional, then decide if the act interfered with, impeded, hindered or confused the fielder. If the runner is legally in the base path and simply running the bases when a collision occurs, he is not out. If he deviates from his path and/or intentionally interferes, or makes malicious contact, he is out. In sliding to a base he must be able to reach out and touch the base with his hand. If he slides into a fielder while more than an arms length from the base it is interference if the fielder is attempting a play. If a runner goes into a base standing up and this act hindered the fielder in an attempt to make a play, it is interference. If he does not slide, he must get out of the fielder's way.

The "must slide" rule is a myth. Only when the fielder has possession of the ball, is the runner required to make a choice of actions. The runner has two choices, slide OR attempt to get around the fielder. He is not required to slide only.
See also; Sliding

Rule 7.09 is the main rule that covers interference.

INTERFERENCE BY THE BATTER

Many people believe the batter's box is a safety zone for the batter. It is not. The batter MAY be called out for interference although he is within the box. The key words, impede, hinder, confuse or obstruct apply to this situation.

An umpire must use good judgment. The batter cannot be expected to disappear. My philosophy is: if he has a chance to avoid interference and does not, he is guilty. If he just swung at a pitch, or had to duck a pitch and is off-balance, he can't reasonably be expected to then avoid a play at the plate. The batter should always be called out when he makes contact and is outside the box. See also Examples of interference

OBSTRUCTION

Obstruction is called when the defense hinders the runners ability to run the bases. There are two different applications of the rule. One causes an immediate dead ball and the other is delayed dead. If a play is being made on a runner who is obstructed, the ball is immediately dead. If no play is being made the ball is delayed dead. A play for purposes of this rule is when the ball is in-flight heading toward the base the runner is heading, an attempted tag, or when the runner is caught in a run-down. The rule book definition is:

"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.

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: 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."

A fake tag is considered obstruction.

The fielder may stand in the base path without the ball, IF, the throw is almost to him and he needs to be there to catch the ball. However, he may not actually block the base until he has possession of the ball. Until he has possession of the ball he must give the runner some way to get to the base.

As with interference, obstruction is also a tough judgment call. Contact between the runner and fielder is not necessary to meet the definition. If a runner must slow down or alter his path to avoid a fielder who is not in possession of the ball or in the act of fielding, he has been obstructed.

If no play is being made on the runner at the time he is obstructed, the play continues. The tough part comes when the play stops. The umpire will award the runner the base to which the umpire believes he would have reached had he not been obstructed. For example: the batter hits a ball in the gap for what looks like an easy double. No play is being made on him. As he rounds first the fielder is in his path and they collide. The batter stops at first. The umpire will award the runner second base if he believes the runner would have made it there had he not been obstructed.

It does not matter where the obstruction occurs. If a runner is obstructed at first base and the umpire believes he could have made it to third base, he will be awarded third. The umpire must be the judge. If, in the umpire's judgment, a runner is slowed down by one step at first and then is thrown out by five steps at third, the out should stand.

An immediate dead ball obstruction is called when obstruction occurs while a play is being made on the runner. For example: a runner on first is attempting to reach third on a hit. He is obstructed by a fielder between second and third as the throw from the outfield is heading toward third. This is a play on the runner. The umpire should call "time" when the obstruction occurs and award the runner third base. Another example is a run-down play. It does not matter which way the runner is heading. If he is obstructed while being played upon in a run-down, he is awarded at least one base beyond the last base he held.

If a runner is obstructed attempting to get back to first on a pick-off play, the ball is dead and he is awarded second.

Rule 7.06 covers obstruction. 7.06(a) is when a play is being made and 7.06(b) is when there is no play being made.