John David Booty said he knew this was different when he ran onto the Metrodome turf for Friday’s preseason game and saw the big NFL logo at midfield.

“That’s what I’ve dreamed about my whole life,” the rookie quarterback from Southern California said. “I’m fortunate to have this opportunity.”

Booty played just about the entire second half of the Vikings’ 34-17 loss to Seattle. At times, Booty showed the promise that made the Vikings draft him in the fifth round, completing 9 of 18 passes for 82 yards, and at other times, he looked like an unsure rookie, taking two sacks, losing a fumble and throwing an interception.

Coach Brad Childress said he thought Booty struggled with the speed of the game, making quick decisions and trusting what he sees. Ball security is a priority, as it is for everybody.

“He’s a quick study,” Childress said. “He’ll get back out there.”

Booty continued to take reps with the third team Sunday, rotating with veteran Brooks Bollinger. He said he needs to correct the mistakes, while continuing to learn, despite limited work in practice.

“There’s a lot of room to grow, that’s the biggest thing,” he said. “You want to play the best game you can, but it’s a big learning experience. It’s just like the first day of practice.”

Farwell, Mitchell out

As expected, linebacker Heath Farwell suffered a ruptured anterior cruciate ligament Friday and will be lost for the season. Farwell, a three-year veteran, was voted the special teams MVP by his teammates and has led the team in special teams tackles over the last two seasons.

“It’s football,” he said. “These things happen. I knew it was a serious injury. I’ve never been taken off the field in a cart.”

Farwell is the third linebacker to suffer a season-ending knee injury in the last three preseason openers, with Chad Greenway in 2006 and Rufus Alexander last season. Farwell said talking with Greenway over the weekend has helped to know what’s ahead.

“I want to be a part of the team as much as I can,” he said. “There’s a lot of hope for this season.”

Childress said that the team will fill Farwell’s position from within, with veterans Vinny Ciurciu and Derrick Pope and rookie Erin Henderson getting a chance.

Childress said that defensive end Jayme Mitchell also ruptured an ACL and will be lost for the season. With Brian Robison sidelined for a couple of weeks with a calf problem, the defensive end position is suddenly a bit thin.

“The tough part of this business is injuries,” Childress said. “Football’s a violent game.”