^^^
THIS!
When I used to referee we called this "preventive officiating" and it is considered very good practice. Tell the second baseman that you noticed in warmups he was dragging his foot across the base BEFORE catching the ball when turning a double play. Let the left tackle know between plays that the linesman says he flexes back a little far and he's dangerously close to being not on the line of scrimmage. I'd do the same in a tournament... talk to him BEFORE he ever actually broke the rule.
This is the best way to handle it. :thmbup:
The worst way is to not say anything at all.