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As members of the NFL’s top-ranked defense gathered in the Vikings’ team auditorium Thursday night to watch the NFL’s annual video outlining rule changes for the upcoming season, it was no secret that what they were about to view could make their jobs more difficult.

After a season in which scoring was down, star players were injured and ratings declined for a second straight year, the NFL figured to respond with measures to facilitate more offense. But as the players viewed some examples of hits that would be penalized this season, the Vikings were taken aback.

"There was one where it was just a great textbook tackle on the sideline, and they said it was a penalty [for the defender lowering his helmet],” safety Harrison Smith said. “There was laughter. It was like, ‘What?’ I don’t know what else you do unless you go in feet-first. There’s a lot to be cleaned up, for sure”

As the NFL unveils its latest attempts to legislate its way to player safety by penalizing helmet use in tackling, players like Smith are forced to adapt yet again to ever-shifting definitions of safe tackling while still finding ways to do their jobs in the NFL’s meritocracy.

The league’s latest iteration of rules changes penalizes players for lowering the helmet to strike an opponent on any part of his body and provides greater protections for quarterbacks after they’ve thrown a pass. It drew an exasperated response from players on social media last week after NFL referees visited training camps to debut the changes, and then put them into practice with a round of dubious flags during Thursday night’s Hall of Fame Game.

Smith sounded hopeful on Friday that the new rules would be enforced differently once officials put them into practice — as league rule changes have been in the past.

Even if they don’t agree with all of the new standards, the Vikings are already at work to play within them. Smith said defensive backs coach Jerry Gray has instructing the team’s secondary on techniques to deal with the change cover and tackle within the NFL’s stricter emphasis on use-of-helmet and illegal contact rules.

One thing that [coach Mike Zimmer] really impresses upon us is, each year, there’s going to be rule changes,” Smith said. “We can complain about them all we want; that’s not going to help us on game day. It’s going to be a penalty, it’s going to help the other team out.

"So, whether we like it or not, try to learn to play within them. At the same time, the way that it is right now, I don’t think it’s clear enough. It would be nice if there were some actual clear-cut rules, and we could start to apply them to the game.”

Zimmer said he was on a rules committee that looked at illegal contact and that he had no issues with the league enforcing it more strictly. Smith, too, seemed less worried about illegal contact and pass interference statutes, which he said are clear enough.

Rules on how defenders can hit players, though, are more irksome.

After referee Pete Morelli said Anthony Barr’s hit on Aaron Rodgers last October — a play that broke the Packers quarterback’s right collarbone — would be called a penalty this season under an emphasis on prohibiting defenders from landing on quarterbacks with all or most of their body weight after he has set up to throw, Zimmer told the official to go back and watch the play again, adding the rule isn’t really any different from the one that made the hit legal a year ago.

Now that he’s out of the pocket maybe it’s changed a little bit this year, but the rule is you’re never supposed drive the quarterback into the ground,” Zimmer said. “You’re always supposed to hit and try and get your body weight off of him. I don’t know why they would come out and say that now anyway. Doesn’t make any sense to me.”

A player in the situation Barr found himself in last October, Smith said, now has to contend with several questions as he approaches a quarterback like Rodgers:

Am I putting my core or back at risk of injury by trying to hit him and contort my body in a way that avoids a penalty?

Do I accept the penalty and fine that could come with a sure, hard hit, or do I hesitate for a split second and open myself up to him pulling the ball down and running by me?

And especially with a player like Rodgers, who makes throws on the run from platforms most quarterbacks would deem impossible, what constitutes him setting up to throw?

He can throw it from any angle, any time,” Smith said. “It happened to be a Vikings guy versus a Packers guy, but take any instance there: They say that if the quarterback is out of the pocket, he’s not a runner, but if he sets back up, now he’s defenseless. And he didn’t set back up. That’s another one that’s subjective. It’s like, ‘Well, he slowed down a little bit, so that’s an initiation of a setup.’ How much verbiage are we going to put in these things and make them completely unrecognizable?”

The day after the video presentation to Vikings players, Andrew Sendejo took part in the Vikings’ walk-through with his hat that read, “Make Football Violent Again,” which the safety has worn for a while but said “applies more now.”

Asked how Vikings defenders reacted to the video, Sendejo said, “Poorly.”

They will adapt, Smith said, because they always do. But as they search for the new nexus between stout, physical defense and clean, legal tackling, Smith wishes the road map was clearer.

I don’t want to be one of those defensive guys that says, ‘No — we want to go hit as hard as we can.’ I want to evolve with the game, too,” he said. "And I don’t know exactly what goes on with those rule changes and things like that. But the way it appears is that people who don’t play the game, or haven’t played the game, make the rules.

And I get it: Offense sells tickets. But there’s certain physical limitations to what you can do with your body. And some of them that we saw on tape, we’re like, ‘You can’t do anything else.’ ”