The guard deserve any punishment he will get.
He probably is 2x time heavier than Mao, he could just hold her with one hand and throw her away or in jail, instead of hitting her IN THE HEAD with a weapon ?
If she was unlucky, she could be dead right now.
And not only that, but after he hit her he wad hysterical and probably wanted to hit her again, you see the others guards who try to stop him.
No need for any sympathy.