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There's more to playing quarterback than knowing what to do after the ball is snapped. Knowing what to do before the ball is snapped can be even more important in what's becoming a pass rusher's league.

Case Keenum and the Vikings' struggling offense got a painful reminder of that late in Sunday's 14-7 loss to the Lions at U.S. Bank Stadium.

The Vikings trailed by seven points and faced third-and-goal from the 3 with 2 minutes, 19 seconds left. Keenum broke the huddle, surveyed the defense and called the worst possible pre-snap protection adjustment a guy could make in that situation.

Sensing pressure coming from his left side, he called for the line to slide left. In that particular protection call, Lions left defensive end Anthony Zettel becomes what the Vikings call the "Hawkeye."

"The 'Hawkeye' is free," said right guard Joe Berger.

Free as in there's no intention of blocking him. And no one did. Right tackle Mike Remmers slid left to block the tackle. Berger slid left and had no one to block.

"You'd like to get to another call if you could," Berger said. "But that's the play that was called."

Sliding left also makes less sense because of how well left tackle Riley Reiff played with very little help all day.

"I thought I saw something and got fooled," Keenum said. "Changed the protection to the wrong protection."

Keenum then compounded the problem by not throwing the ball away. What looked like miscommunication by the line actually was a career backup quarterback making two very big mistakes 3 yards from the goal line and with first place in the NFC North on the line.

"He should have thrown hot," coach Mike Zimmer said. "It was zero-blitz and he didn't throw hot."

Zettel had an easy sack, giving him two on the day. Then, on fourth-and-14, Keenum threw incomplete to Adam Thielen.

Detroit burned only 21 seconds before handing the ball right back. One play later, the Vikings lost their third fumble of the game and, well, that was that.

Their best shot of tying the game was on that third-and-goal play or fourth-and-goal if the ball had stayed at the 3.

"Case has got to throw it away there," offensive coordinator Pat Shurmur said.

The Vikings managed to lose with their defense registering six sacks, forcing seven punts and holding Matthew Stafford to a 23 percent success rate on third downs (3-for-13).

The defense repeatedly got the ball back for the offense. Before the Vikings drove to the Detroit 3, the defense held the Lions to 13 yards on its previous 15 snaps over three possessions.

The Vikings offense took over at its 24 with 8:16 left. The previous five possessions: fumble, fumble, punt, missed field goal, punt.

But even without Dalvin Cook, who left the game with what's feared to be a torn left ACL, the offense still managed to move 73 yards in 11 plays.

Keenum wasn't especially sharp, but showed guts in how he threw into tight windows, particularly on back-to-back completions of 15 and 19 yards to Kyle Rudolph.

Keenum had completed five of eight passes for 55 yards to four different targets when the Vikings reached third-and-goal at the 3. Then …

"I figured I was going to have a clean [shot]," Zettel said. "But I didn't think he was going to hold the ball that long. I got lucky."

This was Keenum's 27th NFL start. He's 10-17, including 1-2 in three straight starts for Sam Bradford.

Bradford's status for next Monday night's game in Chicago is uncertain. With Cook possibly out for the season, the urgency for Bradford to return obviously is immense.

Keenum knows he'll have to be better before and after the snap if he continues to play.

"That [protection call] obviously was a big play in the game, and one I want back," he said. "But I will learn from it and get better. I'm kicking myself for that one."

Mark Craig is an NFL and Vikings Insider. Twitter: @markcraigNFL