He's terribly sorry. Or at least he will be later, when he's still seeing stars from that splashdown. D'Artagnan doesn't immediately notice that they've joined the fray, until the man topples forward. He lets out a 'Ha!' of triumph, and then sees Herian on the other side.

By this stage, he's covered in a whole other layer of mud, and his arms feel like they've been pulled out of their sockets.

"Don't let him up!"

He shouts, and immediately falls on the man's legs. That leaves Herian with the head, which d'Artagnan had imagined might have been the gentlemanly thing to do. That upper body strength might see him wrong, though. He focuses on hooking his arm around one lower leg and throwing his weight against the other, trying to hold the big man down.

All this, while there are two others still stomping around.