Now, I'm not sure if the officer was equipped with this (although I have a feeling he might have) but I think that perhaps the very best way he could have controlled the situation is to use pepper spray on the friend that was pushing him and trying to get her friend away. 

 However, there are some problems with that.  The very first problem is that he would essentially would have had to ask everyone to stop, pull the pepper spray out of his belt ask, "please hold still" and spray.  The spray would have essentially put an end to her behavior and would let him control the situation.  Personally, I would rather get popped in the face than get sprayed.  

 Now given the situation that he was in...I actually think that he held back a lot.  He didn't beat on her excessively, just a surprise hit to the head, and then concentrated on getting handcuffs on the person he was arresting.  Of ALL the excessive force videos I have seen...this comes nowhere near close.