Question about Lining up for a free throw

[mopar60]

I actually knew that one. I have a extra on this though I have thought about.

I don't ever recall seeing anything about contact between players before the free throw. I often see players put there arms out in front of opponents while lined up. Is it legal to touch an opponents prior to the free throw being released?

Do you ever have to tell players to "knock it off" or access any type violation in this regard?

Thanks,