The punch is unexpected enough that Jess has no time to dodge properly, only jerk away in a way that means Spike's fist partly glances off rather than hitting him with full force. It still sends Jess stumbling into bookshelves, but he wastes no time before charging at Spike, attempting to grapple, wrestle and punch whatever part of him that's convenient.

He doesn't actually give a shit about this guy, but he rarely backs down from a fight (especially when someone starts it by punching him), and he may have a lot of pent-up aggression from his current situation. Well, here's something for him to take it out on.