There's no chance of regaining any kind of traction when Charlie keeps his grip and then proceeds to more or less climb up his leg, so there isn't really anywhere for Harry to go to evade the punch.

And it is, needless to say, a hell of a punch. It's enough to slam his head back into the dirt and cause him to lose a few seconds, come back disoriented - and he'd have a hard time remembering what he was doing if Charlie weren't such an obvious reminder.

He can't actually feel his face after the shock of the impact, but now he's got a split lip to match Charlie's battered face, can feel the blood in his mouth even if he hasn't caught up to the pain just yet. There's no quick recovery from that, though he throws a punch right back - sloppy and without much force behind it, but hopefully enough to distract from another hit while he's trying to regain his bearings.