Faster than anything that size has any right to move, though what had he expected? Baker certainly moves that fast. A dragon likely would have, too. So, why not a boar? Childermass knows better than to try and stand his ground in the face of such a charge, but he's also not exactly on par with that kind of speed. He is, in the end, only human (or human enough, anyway).

The good news is he does step aside quickly enough, after waiting for the boar to get close enough to rule out changing direction too fast. The bad news, it's barely. While no tusks hook into him, the boar does manage to snag the cloth of his coat — along a sleeve — and yank it badly enough to throw him off balance with a shout. There's a tearing sound, but not enough to immediately free him...

More like drag him along. That's going to be... fun. Yeah, real fun.