For coaches, preseason football is a valuable tool for evaluating players. For the rest of us, it can be like walking through a roomful of mirrors at the fun house.

What we think we see isn't always what it appears to be. Context in terms of detailed assignments is key, but NFL people aren't always the sharing type when it comes to providing context.

Monday, Vikings coach Mike Zimmer shared some context when asked to elaborate on second-year cornerback Trae Waynes' performance in Friday's preseason opener at Cincinnati. Getting the opportunity to start ahead of the injured Terence Newman, Waynes was up and down with four tackles, a pass defense that was nearly an intercepted deep ball, and some well-talked-about soft coverages that led to short uncontested completions.

While explaining Waynes' assignments in that particular game, Zimmer touched on a point that the rest of us all know but often overlook or can't understand because we aren't given key context: The preseason is real in terms of contact, but not when it comes to winning being the only focus.

When asked to elaborate on comments he'd made about Waynes having the freedom to play press coverage or off the ball, Zimmer said, "There are some rules. But there's also times when I give him flexibility. One time [on Friday], his guy just ran deep. The next play [Waynes] came up and played off.

"They have the flexibility to do that. In real games, I give him, I guess, regulations on when they have to be up [in press coverage] and when they have to be back and things like that."

Had it been a game that counted, Waynes might have been in a different coverage. He was targeted six times and gave up four catches for 46 yards.

The problem wasn't with Waynes' decision to play off coverage. The problem was his depth didn't match Zimmer's guideline for off coverage.

"He was off, but he was even too far off [the line of scrimmage]," Zimmer said. "He's supposed to be at a certain depth."

Zimmer said lining up at the proper depths for press and off coverages, "shouldn't be too hard. He knows he should be here or here. But he wasn't there. That shouldn't take more than a day [to understand]."

It's odd that Waynes would line up at the wrong depth for off coverage considering how much these guys practice. But it's also good when a talented first-rounder with this much raw talent can be developed this thoroughly before being needed to step in as a starter. Especially at cornerback.

"There are some complicated things that go on in some of the coverages, but it isn't so much that," Zimmer said. "It's when they're covering receivers in college, the rules are so much different than in the NFL. And you're getting the best players every week, every day. It's not like every third or fourth game, I get a [challenge].

"Then they can get away with so many things [in college]. They can grab and hit after five yards that doesn't get called. Here, it does. That's the stuff you really have to get corrected. And because of those rules, the techniques are all totally different."