Can you speak up to the authorities about that?

I urge you to talk to a responsible adult - Maybe a teacher or counselor at your school. You have a serious problem that you cannot solve by yourself. … I was a foster parent a long time ago. Your story is like some I have heard. There are legal protections that do not include serving time in juvenile detention. … Running away is an understandable reaction, but where will you run to? That’s what the foster care system is set up to take care of. There are group homes and individual families who take foster children under the supervision of the state. It’s not ideal, but it is safer…

To add to what Chazzster said, when it happens again, get out of the house (not run away, just to get a safe distance from him) and call the police. For many states, it's mandatory for police to make an arrest for a domestic violence call. Juvenile court hopefully will review your case once your stepdad gets a criminal record for DV. Hopefully, your mom can get the help she needs, too.