hagerthorne yes, a punchball isn't necessarily the answer for many (us included) but it can be a help for some.
For DD, when she was smashing things, it was a way to communicate how terrible, how angry and how frustrated she was that she didn't have control over her own mind, that she couldn't feel things, that her instincts were telling her to kill herself. She only did that through the refeeding part of her recovery, when I prepared all her meals because she couldn't make simple choices, and it would only take something tiny (sometimes something imagined) to tip the balance from shouting/swearing to smashing something. It was just grabbing something to hand, no time to think about finding a punch ball. Sometimes the 'something' was me, so I learned to keep my distance. Once she got her weight back to a normal level, she was better behaved but only really behaved better once on anti depressants.
Destruction is not good, but I decided it was better than self harm, and see if there were any ways to limit it. I gave her cheaper plates to smash (but that didn't stop a shard hitting the double glazed door and smashing it too.) mainly though, I tried to find better ways to communicate, and creative ways of expression (music good for her, she likes heavy metal and screamer type stuff, amongst others, though her tastes are much wider now.)
Her weight is low again now and I'm dreading round 2 or this over the next 6 months. Her 16th birthday was horrible, as we were sight seeing in a busy city, we needed to talk about what we were going to do and she lost patience and walked off. Couldn't find her. We split up to look and the family ended up apart for most of the day. When we did meet up, more tears, more arguing and shouting. Horrible. There wasn't anything I couldn't have done any better. She would have liked it if I'd forget it was her birthday and we'd been back in England and with her friends not us. That wouldn't have been better parenting though, and wouldn't have helped her.
She couldn't understand why I cried when she said she wanted to move out, and why I cried again when she said she realised the best place for her was 'at home' with me (wherever that is) and that she doesn't want to move out. I'm compromising; she can go off to her boyfriend's and stay the night, I still need to know where she is, who with, when she will be back.