Old rules number....
7.09e It is interference by a batter or a runner when...Any batter or runner who has just been put out, or any runner who has just scored, hinders or impedes any following play being made on a runner. Such runner shall be declared out for the interference of his teammate.
7.09f applies to a batted ball, but in spirit, it's clear that the rules do not want to reward interference by runners when it makes this statement... "In no event may bases be run or runs scored because of such action by a runner."
New Rules Format 2015:
6.01a(6) restates what I've typed above while 6.01a(7) clarifies how to handle situations with no outs that wouldn't normally end the inning by enforcing the interference by the teammate on the batter/runner. The rule allows for the umpire to call out the runner closest to home to enforce the interference on a batter/runner. A classic play would be the reverse double play where, after fielding a ground ball near 1B, F3 steps on 1B to retire the batter/runner then attempts a throw to another base (commonly 2B or Home) for a double play.
"...the umpire shall call the batter-runner out for interference and shall call out the runner who had advanced closest to the home plate regardless of where the double play might have been possible."
This all assumes that you consider slides like Chase Utley's in game 2 of the ALDS "interference."
Where should the MLB draw the line?
In my opinion, there should be a rule that more closely resembles the NCAA rule, but with a few noted changes:
a. On any force play, the runner must slide on the ground before the base and in a direct line between the two bases.(I would not have this restriction in MLB) It is permissible for the slider's momentum to carry him through the base in the baseline extended (see diagram below). (I would add a stipulation that the runner must remain in contact with the bag upon conclusion of the slide)
92 RULE 8 / BASE RUNNING Exception - A runner need not slide directly into a base as long as the runner slides or runs in a direction away from the fielder to avoid making contact or altering the play of the fielder. Interference shall not be called. (I would not use this exception for MLB. As I stated above, I would allow for the runner to slide in the direction of the fielder as long as the runner is able to maintain contact with the bag upon conclusion of the slide)
1 "On the ground" means either a head first slide or a slide with one leg and buttock on the ground before the base.
2 "Directly into a base" means the runner's entire body (feet, legs, trunk and arms) must stay in a straight line between the bases. (I would remove the straight line wording and change it to "the runner's established path to the base")
b. Contact with a fielder is legal and interference shall not be called it the runner makes a legal slide directly to the base and in the baseline extended
A.R. - If contact occurs on top of the base as a result of a "pop-up" slide this contact is legal.
1. Actions by runner as illegal and interference shall be called if:
2. The runner slides or runs out of the base line (change baseline to established base path) in the direction of the fielder and alters the play of a fielder (with or without contact);
3. The runner uses a rolling or cross-body slide.
4. The runner's raised leg makes contact higher than the fielder's knee when in standing position;
5. The runner kicks or slashed the fielder with either leg.
6. The runner illegally slides toward or contacts the fielder even if the fielder makes no attempt to throw to complete the play.
PENALTY for 1-5 -
1. With less than two outs, the batter-runner, as well as the interfering runner, shall be declares out and no other runner(s) shall advance.
2. With two outs the interfering runner shall be declared out and no other runner(s) shall advance.
3. If the runner's side or collision is flagrant, the runner shall be ejected from the contest.
A.R. - If the bases are loaded with no outs, a double play attempt is made, and interference is called, all other runners must return to their original bases.