The Steelers’ Willie Parker splits Tedy Bruschi, right, and Ellis Hobbs of the Patriots for a five-yard gain in Sunday’s game.

The Providence Journal / Mary Murphy

There’s no denying that the New England Patriots’ defense is struggling to get off the field on third down.

What’s harder to pin down is exactly why the unit is having so much difficulty doing so.

“Generally, it’s something different every dang time,” defensive coordinator Dean Pees said yesterday.

More often than not, according to Pees, the problem is execution.

“That’s what bothered me about this last game [against Pittsburgh]. We’ve got everybody covered but (one) guy, and generally it will be a technique problem more than it was anything else,” he said.

There are times when the Patriots could have been in a better defense, when the wrong call was made for a particular situation, or the offense simply runs a successful play.

But when the difference between a successful third-down stop and a drive continuing comes down to technique, it’s harder to swallow.

“It does become frustrating. It becomes frustrating especially if it’s something that you know you’ve emphasized during the week and maybe you give it up. That’s frustrating,” Pees said. “Sometimes that’s the case, sometimes that’s not the case. Sometimes the offensive player makes a better play than the defensive player, the guy makes a great throw, a diving catch or the ball is two inches off the ground and the guy makes a sliding catch. You have to live with some of those. You’re not going to get them all.

“But certainly we have to do better on third down than what we’ve been doing. That’s across the board — players and me included.”

New England allowed the Steelers to convert 8 of 16 third-down chances, and three of those were third-and-7 or longer. The week before, in Miami, the Dolphins also converted half of their 12 third-down opportunities, including three on one second-quarter drive, when a third-and-10 resulted in a 15-yard completion, a third-and-12 yielded a 20-yard completion, and a third-and-4 was a 10-yard completion.

In the Week Eleven loss to the Jets, the numbers were similar still, as New York converted 9 of 16, including the now-infamous 16-yard pass on third-and-15 in overtime.

The Patriots are now 29th in the league in third-down defense, a stat that becomes more interesting when you consider that they are ninth in first downs against, having allowed 208 in a dozen games.

Prior to the Steelers game, Vince Wilfork nearly guaranteed New England would improve on third-down and red-zone defense, but any improvement wasn’t visible.

“We need to do a better job,” Bill Belichick said on Monday. “(Against the Steelers) it wasn’t the same player and the same situation every time. That’s very important on defense, being able to make those stops on third down and get off the field, and conversely, picking them up on offense. They go hand in hand. We have been working on it. We are going to keep working on it. We are going to work harder on it. We need to do better; there’s no question.”

Fortunately for New England, they should be able to show improvement against the Seahawks, who have one of the worst third-down offenses in the NFL, converting on just 30 percent (45 of 150) of its chances.

Only Oakland (25.3 percent) and the winless Lions (27.1 percent) are worse.

smanza@projo.com