Plate Blocking Question

[chymechowder]

I've searched but couldn't find an answer to this question.

Is there a distinction in the rules (at any level) that allows for a baserunner to crash into the catcher in an attempt to dislodge the ball, but not crash into a fielder at another base?

I'm a USSSA softball umpire, and the applicable rule there is similar--I think--to the rule that seems to govern baseball runners going to 1st, 2nd, or 3rd, namely (and I'm paraphrasing): If a fielder is in possession of the ball and is waiting to make a tag, the runner must slide or attempt to go immediately around the fielder. That is, they can't barrel into a defensive player who is in possession of the ball.

Situations:

Runner on 1st. Base hit to RF. Runner rounds 2nd and heads for third. F9 throws a laser. F5 fields the ball in front of the bag (in the basepath) with the runner still 15 feet away. Runner maintains "ramming speed" (Animal House) and barrels into F5. Ball comes loose and runner touches 3rd. I assume he's ruled out for interference, correct?

Same situation but at the plate. In MLB, at least, the runner is safe at home, right?

(Assume each fielder only enters the basepath after he's in possession of the ball, so there's nothing close to obstruction.)

Is there something in the MLB rules that addresses this difference? Or is it an "unwritten rule" that the runner's allowed to do this when home plate is the destination?

Also, what, if any, are the differences in NCAA or Federation highschool?

Thanks in advance for any responses!