MANKATO – Four longtime NFL officials met with reporters during the day Monday and with Vikings players and coaches later that night to discuss the league's new rules and points of emphasis for this season.

The one new rule that's generating the most interest among the Vikings and their fans is the 15-yard penalty for players who lower their head and use the crown of their helmet to strike another player. In the instructional video shown to reporters and the team, blows by Vikings running back Adrian Peterson and Browns running back Trent Richardson are used as two examples of plays that will now be flagged.

If you're expecting flags to come raining down now there's a rule in place, don't. At least that's the word from the four officials who visited Vikings camp.

"There weren't many of these kinds of hits [last year]," said Laird Hayes, a side judge. "So [the league] doesn't expect a rash of these calls, particularly now that it's a rule. I just think it's one of those incidents that they're adding to so that they can protect these guys as much as they can."

For a flag to be thrown, the hit has to come outside the tackle box and occur 3 or more yards downfield. The player delivering the blow also has to purposely line up his target, lower his head and strike with the top of his helmet.

"If it's close, no, we're not going to call it," said Tony Veteri, a head linesman. "It will be one of the few safety rules that when we have a doubt, we're not going to throw [the flag]."

More for Patterson?

Rookie first-round draft pick Cordarrelle Patterson already has the kickoff return job locked down. But the Vikings also are considering adding him to the mix at punt returner in Friday night's preseason opener at the Metrodome.

Incumbent Marcus Sherels is the frontrunner and safest pick, but the Vikings have to be prepared in case Sherels, a backup cornerback, doesn't make the final roster.

"We have a few different guys there," coach Leslie Frazier said. "We want to take a look at Stephen Burton a little bit. We're probably going to give Bobby Felder a chance. We're debating about whether or not we want Patterson to have a chance to do it as well. Jarius Wright may get an opportunity. So we have a few candidates to potentially take a look at. So we'll see how the game unfolds."

Burton, a receiver, and Felder, a cornerback, are players on the roster bubble. Wright is locked in as the No. 3 receiver. As for Patterson, all he did as a punt returner at Tennessee a year ago was return four punts for 101 yards, including an 81-yard touchdown.

Berger leaves camp

Joe Berger, a valuable veteran because he can back up all three interior offensive line positions, was excused from camp Sunday night for personal reasons. Frazier said he is not sure when Berger will return, but it's not expected to be a lengthy absence.

Working with the second unit at center Monday were fourth-year pro Seth Olsen and rookie free agent Camden Wentz. Olsen is the former Vikings practice squad player who went to the Colts in 2011, started four games for them at guard last season and then returned to the Vikings as a free agent this offseason. Although his best position is right guard, the Vikings also like him as a backup center candidate.

Etc.

Besides the four current NFL officials, the Vikings also had former NFL official Bernie Kukar helping them on the field Monday. A Gilbert, Minn., native who went to St. John's, Kukar was an NFL official from 1984 to 2005. He has helped the Vikings in training camp in the past. Frazier credited Kukar's presence with helping the Vikings cut their number of penalties a year ago.