Stiles' car broke down. he had a large fight with Scott after telling him about killing Donovan. His car starts smoking badly and he gets out, opening the hood and pulling out a wrench. He gets angry, throwing the wrench at the car, busting the windshield. It just so happens that he broke down outside your house, One of his bestfriends.

You hear the noise of the bang and look out your window, seeing that it is stiles.