OBR 6.01(i)

Home plate collisions

Runners may not deviate from their path to lower the shoulder or push through the catcher, and catchers without the ball may not block the runner's lane to the plate. Both halves are enforced: a dirty slide into the catcher means out; an illegal block means safe.

Key points

Runner violation: out, even if the catcher drops the ball — and ejections are possible for flagrant contact.
Catcher violation: obstruction — the runner is ruled safe even if the throw beat him.
A catcher with the ball (or fielding a throw that pulls him into the lane) may legally block.
Contact that is incidental to a legal slide or a legitimate tag is still part of the game.

In a game

Throw from right pulls the catcher up the third-base line; he tags the sliding runner a step before the plate.

Ruling · Legal play. A throw that carries the catcher into the lane gives him the right to be there — only blocking without the ball is obstruction.

Why it moves the scoreboard

Directly awards or erases runs at the plate, and the call swings on which rule the umpire applies — both are replay-reviewable.