Spike shows up uninvited and tries to convince her that she loves him and just needs to admit it. She protests as he forces himself on her, his attempt to make her feel love for him again. ... He becomes distraught both that he attacked Buffy and that he backed off – something the pre-chip Spike would never have done.

Does Spike hurt Buffy?

Spike hit Buffy during an argument and his chip didn't react, so he quickly faked the pain, thinking that it had malfunctioned somehow. Then he tried to attack some girl in an alley, and it went off properly.

Why did Spike attack Buffy?

In "Seeing Red," Spike goes to Buffy searching for forgiveness after having sex with Anya. Buffy is hurt and angry. She tells him she could never trust him enough to love him. He attempts to appeal to her, and when she says no (repeatedly) and pushes him away, he attacks.