Is the guy supposed to wait until he’s on the ground with them kicking him in the face?
No. He could've pushed her away again, or restrained her, for example. Punching an 11yo girl in the face was the problem. Now he's facing charges.
I don't know what happened before the video started, but, if he hadn't punched her, then the girl might've been in trouble - not him. Was that his wife and kid with him? If she had a cell phone, she should've been on the phone with the police.
I've been in worse situations with teens - male teens, older and bigger than those girls - and some grownups. As a woman, though, punching is not what I think of doing. First thing I always did was call the police.