There are a couple of articles on this site that might prove to be helpful:
Ouch!!! How to stop cat aggression toward people. [see the section marked "Play Aggression"]
Playtime Aggression
You can also search the Behavior forum for additional ideas. This seems to be a rather common issue.
Yup! Thank you so much for linking to these!It might be because those replies were from 2008.
I think these are the articles linked.
Cat Aggression Toward People
How To Stop Playtime Aggression In Cats