A runner on second base rounds third after the batter singles to center. About 20 feet from home, out of the corner of his eye he notices a perfect throw to the opposing catcher. The runner puts on the brakes and heads back to third. The catcher pursues. The runner suddenly goes to the ground and rolls into the catcher's shins, cut-blocking him. The runner scrambles to his feet and steps on the plate. Is he safe? Ejected?
For high school and NCAA, I believe this is explicitly disallowed as the cut-block would not be a normal baseball move and would be considered malicious.
- ART. 1 . . . Offensive interference is an act (physical or verbal) by the team at bat:
b. when a runner creates malicious contact with any fielder, with or without the ball, in or out of the baseline.
Rule 8. Section 7. The rules committee is concerned about unnecessary and violent collisions with the catcher at home plate, and with infielders at all bases. The intent of this rule is to encourage base runners and defensive players to avoid such collisions whenever possible.
a. 1) The runner must make an actual attempt to reach the base (plate).
PENALTY—If the contact is flagrant or malicious before the runner touches the base (plate), the runner shall be declared out and also ejected from the contest.
My speculation is that this is not specified in MLB rules because it has a much lower chance of success and has therefore not been as much of a problem (except at home plate). I don't believe there's an explicit rule here, but there's also not an explicit rule against fighting and you can get tossed for that. I have no evidence for what would happen in an MLB game today.
A cut-block under college or high school rules would considered and called "flagrant" or "malicious" contact in the eyes of most (if not all umpires). This is specifically not allowed in most leagues and at minimum makes the runner out if not ejected.
In the Major Leagues, although I can't recall this happening ever, Rule 7.13 ("The Buster Posey Rule") or Rule 6.01 ("Interference, Obstruction, and Catcher Collisions") most likely would take effect (albeit somewhat loosely) and the runner would be ejected.
Here is 7.13,
A runner attempting to score may not deviate from his direct pathway to the plate in order to initiate contact with the catcher (or other player covering home plate).
If, in the judgment of the Umpire, a runner attempting to score initiates contact with the catcher (or other player covering home plate) in such a manner, the Umpire shall declare the runner out (even if the player covering home plate loses possession of the ball).
Notably, however, the runner is entitled to do some things that involve contact with the catcher that isn't necessarily seen as "flagrant". For example, if the runner lays down all of the sudden in order to miss a tag, then the catcher trips over him, in the eyes of most umpires, this is fair game.