He sees the hesitation, making him frown. She shouldn't be hesitating, she should have immediately followed up and tried to go right for his face or something, not stand there even for half a second to consider it. From there, he can see all the ways he could counterattack, really not a good idea on Bulla's part. Maybe it was because she was hitting her father, that caused her to hesitate- so he'll make her regret that. Just because he was her dad doesn't mean that in this situation she should be holding back at all.

He continues to block when she resumes, but he's going to start moving a little faster now. And he'll be looking for his own opening to parry a punch, with the intent of making her defend herself with his own assault.