My understanding is that "practices" with the coaches start 29 days before the first game. In the summer, anything on the field has to be run by the S&C coaches under certain rules. Any sessions where players line up against each other are players only.
They're trying to get as much done as they can within the rules. But it's all important, maybe even decisive for the season. A team that only works hard when the coaching staff whips it out of them probably isn't going to be that good.