Kenickie was in a gang, the T-birds. Did you care? No. Did you hang out with them? Sadly. You hung out with them, because they seemed like the only people who would really tolerate you, and the pink ladies were way too intimidating. You settled for this gang of high schoolers.
Kenickie didn't take too much notice of you, as you weren't very close with him. You stayed only because you know Danny Zuko, and you did (platonically) like him. Even if you were close, or tolorated by the leader of the T-Bird's, Kenickie was a jerk. He'd mess with you. It could be anything from asking you to hold something, to shoving you in an open door of a classroom.
But even if he did mess around with you, he didn't want other people to be mean or bully you. Why? Because, you barely did anything to get on anyone's bad side, and also, Kenickie knew he was a prick. He did.
So, now, you and the T-birds were walking to your class. The hallways were crowded, so it was a bit hard to walk, so you accidentally bumped into a girl. A mean girl.
She looked at you, with a "What the fuck" look. You apologized, and said you didn't mean to. But the girl kept pushing, her voice getting just a bit higher.
Kenickie saw this, and he reached for your hand. When he grabbed your hand, he pulled you to his left side, away from the girl. "Hey, calm it, yeah?" He said to the girl.