Collisions at home plate are always a possibility. Here are the ways that the NFHS rules differ from the Official Baseball Rules on potential collisions at home plate.
A runner cannot initiate a collision with a fielder, even if the fielder has the ball between the runner and the base he is trying to get to. If the runner does so, it is interference.
A catcher who is not in possession of the ball, even if he is in the act of receiving a throw that is nearly to the plate, cannot be in the runner’s path. This would be obstruction.
If the play at the plate is a force play, the runner must observe the force play slide rule or risk his out for interference and another out on the other runner who would have been played against. A runner is never required to slide, but if he does so he must not violate the rule for a legal slide, which includes sliding directly into the base or away from the fielder.
If a runner scores on a force play attempt at the plate and then interferes, he is out, his run is nullified, and any other runner played against is also out.
[OBR: permits a collision that is incidental contact (not avoidable; no player is at fault; both players are doing what they are expected to do). Thus if the catcher has the ball or is receiving the ball and is blocking the plate and the runner just tries to get through and score, it is legal. There is no force play slide rule. Any runner who scores cannot have his run taken away for interference; the other player played against is out.]