Young people with Autism and Asperger's often find their feelings and their inability to express them adequately extremely frustrating - and the only way to deal with this is to vent them in aggression because they can no longer be controlled - imagine a shaken up fizzy drinks bottle as a metaphor. This is usually towards the person who is closest to them and who they feel safest with in terms of connection - hence You!
With any behaviour it is a form of communication - a way of expressing self when there are no words to do so. This means that it is difficult to punish - and I wouldn't suggest you do so. My general rule when dealing with behaviour issues is to try as far as possible to ignore bad or difficult behaviour but conversely make a big thing out of good positive behaviour. The exceptions are if the behaviour is one which has or will harm your child, someone else, or someone else's property – and distraction is often the best policy.
When we communicate in whatever way it is because we need attention. If we do not get the attention we need then frustration may lead to using more negative behaviour to get it - any attention is better than nothing! This is why, although it may take some time, the strategy of ignoring the bad and promoting the good works.
In addition, give as much love and positive reinforcement as you can to your child - whenever you can every day. They need it even more than most.
