Halfway through the NFL preseason, the Vikings haven't lowered their heads.

But they sure are scratching them as they try to understand the league's new rules on player safety.

"At the end of the day, this whole rule deal is sketchy, at best," Vikings defensive end Brian Robison said after Saturday's 14-10 loss to Jacksonville at U.S. Bank Stadium. "I don't think we know exactly what's supposed to happen. … I think we're all confused about it. You ask the refs and they might be confused about it."

In two preseason games, no Viking has been flagged for lowering his helmet to initiate contact. Opposing teams have been called for it three times, including twice on Jacksonville.

But Vikings backup linebacker Antwione Williams was penalized for what, apparently, was a violation of another point of emphasis this preseason: driving the quarterback into the turf.

With five minutes left in Saturday's game and the Vikings leading 10-7, Williams made what appeared, in real time, to be exactly what the NFL wants in a sack. His head was to the side of Cody Kessler. Contact was initiated by the shoulder.

The perfect midfield sack to secure field position late in a game, right?

Not exactly. Roughing the passer. Fifteen-yard penalty. Goodbye, field position. Goodbye, lead. Hello, confusion, controversy and conflicting views on the future of the NFL.

Coach Mike Zimmer was angry. He yelled at the officials while pointing to the replay on the big screen.

But, by the time he spoke to reporters after the game, Zimmer was in agreement with the officials.

"If [Williams] had just rolled [off Kessler]," Zimmer said. "But he kind of pumped him into the turf. So, I think that was a good call."

Zimmer probably knows that any complaining he does about the new rules just makes it tougher to continue teaching the players how to accept and abide by them. Asked how tough it would have been for Williams to do what Zimmer explained, the coach shrugged and said, "That's the rule, so we have to do it."

Williams accepted the penalty as a learning experience in a new league order.

"I just have to try and lay to the side more," he said. "Just try to get used to the new rules. The refs are trying to get used to it, as well. We're all in the learning process right now."

The Jaguars were flagged 13 times for 140 yards. Four of those were 15-yarders for the kinds of hits the NFL wants out of the game. Besides the two for lowering the helmet, Jacksonville was flagged for a blind-side block and hitting a defenseless receiver.

The first flag for lowering the helmet came early in the first quarter when cornerback A.J. Bouye initiated contact with Vikings fullback C.J. Ham. Ham also lowered his helmet to brace for contact right after catching a short pass.

"That could have easily been called on me, too," Ham said. "But playing the game, the first thing you do when bracing for contact like that is to lower your whole body. I suppose both of us could have done a better job keeping our heads up in that situation. We're all learning."

Bouye told reporters after the game that he was just trying to go low so he wouldn't be run over by a bigger player. He also said Ham should have been penalized as well.

Another week, another feeling-out process for the players, coaches and officials.

"It's leading to less aggressive play," Robison said. "Now guys are slowing up on a play, they might get hurt. To me, if you slow up on a play, it's going to weaken the strength of our game.

"And I understand what the NFL is trying to do. They're trying to cut down on a lot of the head injuries and stuff like that. But it's just confusing, to be honest with you."

Mark Craig is an NFL and Vikings Insider. Twitter: @markcraigNFL. E-mail: mcraig@startribune.com