I don't think Xander would have stepped in because I agree with Taake that when someone Xander doesn't know is in trouble, he wouldn't really get involved. However, if Lance was a friend of his, Xander would have stood up for him against the bullies.
Did you guys forget that Xander, just learning that vampires were real, followed Buffy to the sewers to save Jesse? He was really upset when Buffy wouldn't let him help. Willow was too scared she wanted to sit down even though she was already sitting down, Xander, on the other hand, only thought about saving Jesse. And that happened in the very first episode, so there was no time for Buffy to influence him, which means that Xander has always been a brave character.