So I recently attended a HS football game here in the area. The particular venue I was at allows for fans to stand rather close to the field since there is not a lot of seating.
There was this fan from the visiting team standing not too far from me. He was very enthusiastic, but he kept it clean and was not vulgar in any way. He wasn't talking to the refs or to the players or anything like that.
When the home team had the ball he kept yelling "SACK! SACK! SACK!".
Anyway, an administrator from the home team walked over to him and told him that it was illegal for fans to yell anything while a QB is under center. And that if he continued to do so, he would be asked to leave the game and leave campus.
Never heard of such a rule.