[IREFU2]

I had a play at the free throw line. I was the trail and the defender was standing directly behind the free thrower during a two shot free throw. I could see his lips moving, but really couldnt hear him say anything. After the first attempt, I made him back off and move from behind the thrower. Is there any kind of rule about this? I know about the disconcertion rule, but what about being directly behind the thrower???