Spike sputters. "I-- that was-- I was making sure she didn't turn into Fred and endanger us all!" Or something similarly noble.

It's clearly time to start the fight, but for all he's been assuring Buffy that she won't hurt him and it'll be easy, he's got his own doubts. For so long now Buffy's been someone he refuses to hurt. Though he knows he can't hurt her, even trying goes against his instincts. Still, he throws a punch towards her at half speed.