Nickey lost his temper a bit as he climbed out from under Mruczkowski and threw a punch at him. Now, it's bad enough that Nickey was going to throw a punch about two feet in front of an official's face, but unfortunately, Nickey also punches about as accurately as Matt Moore(notes) throws. He missed Mruczkowski and ended up landing a straight right to referee Bill Levy's chest.
I think my favorite part of all this is that Nickey seemed upset at being ejected -- as if there's some other possible outcome after striking a ref. Intentionally or not, the tolerance level on that sort of thing is way, way low.