My mom, before she died driving drunk (with me in the car!), had a husband (stepdad to me) who used to beat her too. He hit me once, when I was 10, and broke my collarbone. I told him if he ever hit me again, I'd kill him, and I meant it, and he knew it, and he never hit me again. He did hit my mom again though, so I stabbed him in the back with a fork, then while he was stealing her purse, I went outside, let all the air out of the tires on his car, then called the cops on him. He was a bad, bad man and died himself when he was just 28, of a rotted liver from drinking.

You think you can't do anything at age 15, but actually you probably can. At that age you're a juvenile. If you 'accidentally' push him out a window while he's beating your mom, I don't think anyone would do anything to you. Not that I'm advocating you do something like that. It'd be a lot better if your mom realized that hanging with someone who beats her is not in her (or your) best interest. I'm just saying, maybe you have more options than you think you do. Personally, I wish we'd had steaks the night I stabbed my stepdad with a fork, because then I'd have had a steak knife handy instead of that fork, and he might not have gotten up again if I'd had a knife. He almost beat my mom to death that night, so if I'd killed him protecting my mother, I don't think I'd have been charged with anything. A 50-pound 10 year-old boy being accused of killing a 200-pound adult man would make a pretty bizarre picture in a courtroom. Heh.