I will assume you know the basic. Use the S mode instead of the A mode as your boy is running around. From what you say, I think it might be due to poor ligthing condition.
I suggest you increase you ISO value to compensate for that.
If you want more in depth detail do let me know.
yes pls ... how to compensate the ISO....
also notice A and S mode dont auto flash den how would i know if flash is needed...