J.G.
My daughter did until right around that age. We worked hard together to replace the behavior with others. She picked pinching. I told her that wasn't acceptable, so I taught her to clap,or stomp her feet.
I find 4.5-5 year olds to be very aggressive. They are all about fairness, so the lash out a lot.
I have a zero tolerance policy for anti-social behavior, so if she lashes out, we head home, she goes to her room, etc.