The man at the epicenter of the Buffalo Bills’ season-long defensive struggle stood silent Friday.

Embattled defensive coordinator Dave Wannstedt turned down an interview request with The News following the Bills’ final practice of the season. It’s possibly the final one he’ll ever get.

It’s been a trying year – to put it kindly – for Wannstedt in his first season as coordinator. His unit is languishing at or near the bottom of several key statistical categories, and threatening to set franchise records for defensive futility.

“The job is production and winning and we haven’t gotten there,” coach Chan Gailey said this week. “We knew that we were going to have some work to do to get it done and haven’t gotten it done yet.”

Nowhere is that more evident than on the defensive side of the ball.

Led by Gailey and quarterback Ryan Fitzpatrick, the Bills are 19th offensively in yards and 20th in points per game. Those numbers are below where the Bills hoped to rank, but not drastically different than expected.

The same can not be said for the defense, which has underachieved to a significant degree. Consider:

• The Bills have allowed 5,474 yards this season, an average of 364.9 per game. If they allow their season average Sunday to the New York Jets, they’ll finish with 5,839 yards allowed, which would be the second most in franchise history (trailing only the record of 5,938 last year).

• The Bills have allowed 426 points. If the Jets reach 29 on the scoreboard Sunday, the 2012 Bills will own the record for most points allowed, breaking the 454 given up by the 1984 team. Buffalo’s average of 28.4 points allowed per game is 31st in the NFL. The team allowed 27.1 per game in 2011, ranking 30th in the league.

• The Bills rank last in red zone defense, having allowed touchdowns 38 out of 52 times, or 73.1 percent of the time opponents have reached their 20. Last season, when they also finished last in this category, the Bills gave up touchdowns 64.4 percent of the time.

• The Bills’ third-down defense is last in the NFL, allowing opponents to convert first downs 44.3 percent (85 of 192) of the time.

• The Bills are the first team since the 1986 Jets to allow at least 45 points in four games this season.

Buffalo starts five players – cornerbacks Aaron Williams and Stephon Gilmore, linebackers Kelvin Sheppard and Nigel Bradham and defensive tackle Marcell Dareus – who are in their first or second years in the league. Both Dareus (third overall) and Gilmore (10th overall), however, were taken with high first-round draft picks that bring with them heightened expectations.

Much of the criticism surrounding Wannstedt has had to do with his scheme, which can best be described as “vanilla.”

The Bills blitz (send five or more pass rushers) less than they did last season, when they ranked near the bottom of the league under coordinator George Edwards.

Wannstedt has relied on his front four to pressure the quarterback, with mixed results. The Bills have 35 sacks, which is tied for 15th in the NFL. Just four of them have come from players not on the defensive line (two each from linebackers Nick Barnett and Kelvin Sheppard).

Opposing quarterbacks have made it a point to get the ball out quick against the Bills, which can negate even the best four-man rushes.

Several times this season, players have mentioned not failing to stay “gap sound” as a reason for the defensive failings, particularly in the run game. The Bills looked like they had turned a corner in that regard from Weeks 10-15, when they held teams to an average of 78.4 yards per game and 3.1 yards per rush.

The last two games, however, the run defense has been gashed for 452 yards. Seattle in Week 15 and Miami to a lesser extent last Sunday had success in running the read-option play. The inability to get the front seven on the same page defensively is a huge knock against Wannstedt.

“I really think we’ve played a little bit more tentative the last couple of weeks than we did there for a while,” Gailey said. “I thought we were starting to hit our stride and make a lot of progress defensively.”

With Wannstedt declining an interview Friday (he wasn’t the only one, as General Manager Buddy Nix postponed his own radio show), players are left to explain the defense’s failing.

“What this game boils down to is execution on game day,” safety George Wilson said this week. “That’s something that the coaches don’t do, they’re not out there playing on Sundays. That is up to us as players to execute on Sundays. But for us to be where we are I don’t think the blame lies on one particular area. I think we all have to take ownership of it and that’s everyone in the organization from top down.”