Ever Seen This Before?

[Rufus]

Former coach whose son played in a 13U scrimmage yesterday. The opposing pitcher for the second game did not engage the front of the pitcher's plate when getting signs or pitching, but maybe placed his right toe on the very back left edge of the plate (portable mound so no "dugout" in front of the plate). At first it didn't appear he was engaged at all while receiving and/or pitching, but he never did try to quick pitch or deceive/pick-off in any way other than pitchers normally do when they engage the front of the plate.

The PU questioned him about it and he said he was touching the plate (only one umpire working for the scrimmage).

Anyone ever see something like that? I've not had a chance to review any rules on it but I'm thinking if he's engaged with any part of the plate he's ok. Definitely a first for me as either spectator or coach.