That's not exactly accurate. Allen is off to an abysmal start, if you look at sacks as the only measure of success. Currently he is on pace to finish the season with only eight sacks. Last year at this point he already had 6.5 sacks, and was only held without a sack in only three games all season. So far this season he's been shutout twice in four games.
The problem is not with Jared Allen. His lack of sack production is not due to age or the defensive line rotation that is giving him a few more snaps on the sidelines. Plain and simple, the Lions, like every Vikings' opponents this year, has been rolling extra help to slow down the NFL's leading sack producer since 2004.
As you can see in the pre-snap picture, the Lions lined up in an offset eye formation with the fullback to the left of Stafford.
As Stafford drops back in the pocket, the fullback is prepared to help protect his blindside by chipping on Allen. On this play, Stafford was able to drop back eight yards and deliver a long pass downfield within two seconds. The result was a defensive pass interference penalty for 56 yards.
The Lions also used extra bodies on the left side of their line to help the left tackle Jeff Backus slow down Allen.
A week earlier against San Francisco, the 49ers used a similar formation with a tight end and a running back to slow down Allen.
Quarterback Alex Smith rolls away from Allen providing an eight-yard cushion between he and the two-time NFL sack leader.
The result of this play was a short pass to Michael Crabtree for six yards. Smith released the ball within three seconds, not giving Allen or any other Viking time to apply any pressure.
The Colts opened their first drive in Week 2 with extra protection the the left side of the line with two tight ends.
Before the snap the Colts motioned Reggie Wayne to Allen's side for even more protection. On this play, Andrew Luck handed the ball off to running back Donald Brown.
The Colts would use the play-action pass later to slow down Allen. On the following play the Colts used a tight end in the backfield, moving him to Allen's side for extra help.
With three bodies in front of Allen, he finds his path heavily barred. This time Luck fakes the handoff. The move lures Allen to the middle of the line to stop the run.
It results in plenty of separation between Luck and Allen.
With plenty of cushion, Luck had five seconds to set up in the pocket and complete a pass downfield to Donnie Avery for 41 yards, putting the ball on the Vikings 3-yard line.
With this extra attention paid to Allen, the rest of the defensive line needs to step up and take advantage of single blockers in front of them.
On the play in the Detroit game that Allen got his sack, the Lions failed to provide extra help.
On the play Stafford fakes the handoff and drops back; the play takes too long to develop and Brian Robison applies pressure, flushing Stafford out of the pocket.
On this play, Kevin Williams is forced to the outside and contains Stafford, forcing him back into the middle, right where Allen is waiting.
Even though Allen is credited with the sack, it took the effort of Robison and Williams to contain Stafford, as well as the defensive backfield providing enough coverage to prevent a quick release.
Yes, Allen is off to a slow start, sack-wise, but he is still an effective defender. His play has the Vikings' defense ranked eighth overall in the NFL in yards allowed, and seventh in points allowed—something the defense couldn't claim when he was racking up 22 sacks.
Allen, like most fans, are probably willing to trade the sacks for wins.