Charlie hadn't expected the attack nor the help. He really wasn't expecting anything other than a few cuts and bruises from this. He didn't mind them so much because he understood what he was going into. It was a fight, fights meant pain and suffering for someone.
"I..." the detective started to answer, but the frat boy was already off into the fight. He watched the scene around him for a little bit, protecting himself with the least amount of effort and violence. He only partially understood why he felt the need to help the boy; Logan was having a hard time adjusting perhaps, and he also had some other issues. These issues spoke to something in Charlie, so he'd help as much as he could.
Before Charlie could make it to Logan, there was a shout at one of the doors, followed by more shouting. The main word in the shouting? "Police!"