I baby sat an autistic boy once, who tried to brake my finger because i pointed at something, and when i said something he didn't like he jumped on me... with his knees. I just told him that he needs to calm down, and tried not to anger him. Make a compermise with the child, say you will do what they want in 10 minutes, and then do something to get their mind off of it, with any luck the child will have forgotten what they wanted in the first place. Autistic kids are hard to deal with, you just need to be patient and be clear that you are the one in control :) good luck
My next door neighbor has 2 autistic children and i've learned that they just don't like anything that they aren't interested in. You try to do things they like to do, and if they scream at you or don't do something right, you tell them no and take away a favorite toy. If you teach an autistic child from the beginning that what they are doing is wrong, they will learn to listen better. How old is the child you are talking about?
I would say just let them get there anger and agression out or get them an at home therapeutic class.