Hello paulponty,
I'm sorry to hear about your son's behaviour. Individuals on the spectrum can often display behaviour that may be challenging. There will generally be a reason for this and it is important to try and understand the trigger for the behaviour when developing strategies.
You may like to have a look at the following link for more information on behaviour and strategies:
http://www.autism.org.uk/living-with-autism/understanding-behaviour.aspx
We also have a page on our website that centres around physical challenging behaviour. Including the possible causes, as well as strategies and interventions you can adopt to improve his behaviour: www.autism.org.uk/.../challenging-behaviour.aspx
You may find it useful to have a look at our behaviour guidelines and general behaviour page:
http://www.autism.org.uk/about/behaviour/guidelines.aspx
http://www.autism.org.uk/about/behaviour.aspx
Hope this helps. All the best,
Karin Mod