– Mike Zimmer put in a full day and then some as the first training camp of his NFL head coaching career began unexpectedly around 1:30 a.m. and included another twist that saw one of his best players sidelined and listed as day to day because of a foot injury.

“I’ve always told [the players] they have to be aware of every situation,” the first-year Vikings coach said with a smile.

From the early-morning fire alarm that scattered players into the street outside Sears Residence Hall to the late-afternoon news that receiver/All-Pro kick returner Cordarrelle Patterson was held out of practice as a precaution for a minor injury, Day 1 of Camp Zimmer was interesting, considering that full pads and high-speed collisions aren’t allowed per NFL rules until Sunday.

Here are four snapshots from Day 1 at Minnesota State Mankato:

Unexpected noise

When it comes to experience, Matt Cassel trumps Teddy Bridgewater in years (32-21), training camps (10-1) and, as it turns out, middle-of-the-night fire alarms during training camp (2-1).

“I was sleeping well until that alarm went off and woke everybody up,” Cassel said. “I think coach set that off to see if we’re mentally tough.”

Zimmer denied any involvement before saying, “But, come to think of it, I wish it was [me]. I’ll have to use that next year.”

The hard-nosed coach did, however, make sure everyone was booted from the building despite the false alarm.

“I tried to lay down as long as possible,” said Cassel, “but somebody came and knocked on my door and told me I had to evacuate.”

Asked if he’s ever experienced anything like that, Cassel said, “Actually, I have. I had another training camp where that happened. But I didn’t leave the room that time.”

Just wait, Mr. Rodgers

Like so many of us, Brian Robison blinked and became an elder statesman.

“It seems just like yesterday that I came into this league,” said Robison, now 31, in his eighth season and the only returning defensive line starter. “And now I’m kind of the old guy.”

But the old guy had a bounce in his step as he left the field following the first walk-through of training camp. After seven seasons in the same read-and-react defensive system, Robison said each practice now brings added excitement over Zimmer’s more aggressive philosophy.

“I don’t think our [previous] defense got outdated,” Robison said. “I just think sometimes you get schemed against and it doesn’t work in your favor.

“We play Green Bay and Chicago and Detroit twice a year. When they see your defense over and over and over again, heck, there were some times when we’d line up and Aaron Rodgers is calling out our defenses as we were lining up. I think the thing with Zimmer’s defense is he’s going to definitely keep them off balance because there are so many disguise looks and so many ways we line up in the defense, even with different fronts. It’s all over the board.”

Cassel’s job to lose

The pecking order at quarterback is obvious to any camp observer. Cassel, who completed six of 10 passes during 11-on-11 competition on Friday, is No. 1.

Bridgewater, who was 5-for-8, is No. 2 but on the rise. And Christian Ponder, who was 1-for-1, remains a distant third.

Thursday, Zimmer called Cassel his No. 1 quarterback “heading into training camp.” The obvious meaning, which Zimmer spelled out on Friday, was things can change before the season opener.

Asked if he was expecting Zimmer to call him his “No. 1” publicly, Cassel said, “I would be lying if I said I wasn’t. I worked hard this offseason. But I still have to earn this thing.”

Twitter kerfuffle

The first serious injury of the Zimmer regime became the coach’s first social media kerfuffle when Chase Ford, one of the promising youngsters competing for the No. 2 pass-catching tight end spot, tweeted Thursday night about his recent surgery to repair a stress fracture in his left foot.

Zimmer said he doesn’t tell players not to tweet, but he made it clear that there are boundaries that do not include injury information.

“We actually had that meeting [Thursday] night, and then it gets tweeted, so we’ll have a discussion,” Zimmer said. “[Ford] must not have been paying attention in the meeting. I will fix those things.”

All in a day’s work for a 21st-century NFL head coach.