EDEN PRAIRIE (AP) — Since his NFL career started seven years ago, Jared Allen has celebrated each sack by dropping to one knee, twirling his arms and thrusting them into the air — pretending like he’s roping a calf.

But before his most recent game, Minnesota’s All-Pro defensive end learned his signature celebration is against the rules and subject to a 15-yard penalty, plus a possible fine from the league.

Next time, Allen will have to improvise.

“Actually I’m going to carry some cardboard with me and slide it underneath my knee going forward,” Allen said after practice on Monday, with a big smile. “It’s legal, right?”

The Vikings were informed by new NFL vice president of officiating Carl Johnson before their Sept. 26 game against Detroit that Allen’s demonstration, in which he touches the turf with his knee, qualifies as unsportsmanlike conduct under the league rule that prohibits players “from engaging in any celebrations while on the ground.”

According to the NFL, Johnson is trying to enforce the rule as it’s written.

Allen, who has paid his share of fines over the years for various hits, said he felt a little unfairly targeted because of all the celebrations that occur in a typical game.

“I guess rules are rules, and as long as I don’t put my knee on the ground I’ll be OK,” Allen said.

He added: “I wouldn’t be too mad, but it’s the 15 yards that really get you. It’s the penalty. The fine? I’ll eat the money.”

Allen vowed not to abandon the act altogether.

“But I’ve got to get to the quarterback first, though, right?”

Through three games, the Vikings have only four sacks. Allen has one. As a team, they’re 27th in the league in sacks per pass play.

Fellow defensive end Ray Edwards expressed his frustration with the league for a couple of fines he got last week for hits in the game against the Lions.

“I think they just hate the Vikings. We get held more than anybody, but we don’t get the calls,” Edwards said. “I guess we’re outlaws or something. So I guess that’s how it goes.”

The Vikings returned from their bye week on Monday, with two starters still unable to participate in practice. Center John Sullivan watched from the side, and tight end Visanthe Shiancoe jogged on his own. They each hurt leg muscles against Detroit, but the Vikings have not specified their condition.

Coach Brad Childress said both of them stayed in town last week so they could treat their injuries at the team’s facility.

“They’re making progress,” Childress said.

Already trailing Chicago and Green Bay by two wins in the NFC North, Minnesota faces a challenging month. The Vikings play road games against the Jets, Packers and New England Patriots, with their only October home contest a game against the Dallas Cowboys in a rematch of last season’s playoff game.

Like any football team that listens to the coach, the Vikings are insisting they’re not looking ahead. Allen sounded convincing when, during an answer to an unrelated question about the Jets, he wished aloud for a game against the struggling Buffalo Bills.

The Vikings actually do play them, on Dec. 5.

“Oh, do we? Where we playing ’em at?” Allen said, laughing.

The game is in Minnesota.

“Oh, hey, what do you know?” he said, laughing even louder. “So, like I said, I don’t even know who we play after the Jets.”

It’s always difficult, and dangerous, to predetermine in the NFL which games will be hard and which ones will be easy. The fortunes of teams frequently shift in this unpredictable league.

“Everybody’s going to have their ups and downs,” Allen said. “We’re starting slow, but we’re starting to get guys back which is nice. Hopefully we can run away with it again. That’s what we want. But it’s going to be a grind. Right now it is. We’re going to have to catch the Bears and the Packers. We’ve got to keep grinding and hope other people slip up.”

Success for this team, at least on defense, starts with a strong pass rush.

“They come in bunches,” Allen said. “So we’re not worried about it up front. I think we’re doing some good things.”