You won't find it on a sign, in a playbook or as part of any Vikings code of on-field conduct. But if you're a defender at Winter Park, you know the rule.
"I would say it's one of the unwritten rules," defensive end Brian Robison said. "Bottom line, in practice, stay away from Two-Eight."
That would be No. 28. Adrian Peterson.
But sometimes there is a significant problem with that rule. It begins with the fact that Peterson is possibly the NFL's most physical player and ends with the fact that he loves turning his 6-1, 217-pound frame into a contact-seeking projectile that's too darn fast to avoid, even in practice.
"That's the thing," safety Harrison Smith said. "Sometimes, when there's a collision, it's because we're trying to move and he won't let us.
"You can kind of tell when he's fed up with not having any contact. That's when he'll start running at you instead of away from you."
With no preseason action, virtually no practice contact and Sunday's regular-season opener at St. Louis only two days away, Peterson definitely has reached Defcon 1 when it comes to his desire to smash someone. And he admits there are times in practice when he crosses the line.
"It's kind of like a one-sided thing," Peterson said of the unwritten no-contact rule. "A lot of defensive players come to me and complain about it because I do look for contact, so I kind of give the guys a shoulder or two from time to time. I know guys like Harrison Smith, he's not going to back down, so it kind of rubs him the wrong way sometimes. He voices it to me. Nothing that he's mad about, but it is what it is."