We called this penalty no less than 6 times in two youth games this last weekend. During the first game, the offending team's coach asked what the penalty was for, when we told him he said "Oh man I forgot that was a penalty!" Evidently this reminder wasn't enough to keep his players from doing it twice more.
There was one hit during the last game that in hindsight, I should have ejected a kid for. I guess I was a little hesitant to pull the trigger as a new guy.