According to what I have seen, the officer had "swelling" on the side of his face. That's about all the details.
Doesn't necessarily prove he was beaten by MB, however. It could be that the door to his own vehicle hit him on the left side of his face as he tried to exit it, when the door either bounced off or was pushed back by MB.
Interesting that it’s not his whole face but only “the side of his face” — probably the left side of his face where his left arm was holding the kid by the neck.