Question: Free Throw Violation?

[djsteele95]

I am a referee in a youth league that tries to go by high school rules other than a few variations for the youngest kids. League is for 5-12 year olds. We have run into an unusual situation and can't decide whether it is a violation or just bad sportsmanship. Here it is: Can the opposing team lined up in the blocks during a free throw attempt yell and scream at the shooter. The standard stuff, "miss it", "hey shooter", etc. while he has ball in hand. I never see this happen during high school, college or NBA games so I have assumed it was a violation. However, I can't find a rule that says so. If it isn't, then we will probably add the rule for our league as we want more focus on learning and less on winning. I would just like to know if there is a rule on this situation. Thanks.