I'm not super familiar with police protocol, but I'm pretty sure neither video illustrates what they generally teach you in the academy. On the street, I can understand going right to the fists, but he is trained to use his other tools(taser, baton, ect). I think it shows he is not trained that well if he immediately resorts to punching her.
As for the jail cell, there is no context, but I'd say that is not proper procedure at all. Running in and swinging when you have a prisoner in a quasi controlled environment with various tools and resources at your disposal seems like he just felt like punching her in the face.
In the end, he won't get in trouble, but he should be re-trained on proper procedure and let chain of command do the rest.
Edit: just watched the other video. Cop definetly sucks at his job and needs to spend another year at the academy. Take the bitches, grab em, shove their face into the hood and stick bracelets on their wrists. At no point did he seem in control of the situation.