While the best NFL teams are making plans for the playoffs and playing their best football of the season, the Washington Redskins are once again plodding their way toward the finish line. It’s not like September, October and November have been particularly kind to the Redskins in recent years, but the month of December has been especially harsh.

Since Joe Gibbs left Washington after the 2007 season, the Redskins have posted some of the worst December performances of any NFL team. Every other franchise except the St. Louis Rams has won more late-season games than the Redskins in that period. In fact, the Rams and Redskins are the only two teams to total fewer than five post-Dec. 1 wins over those four years. Since the Redskins’ last playoff berth, Washington is a combined 3-13 after Dec. 1.

With losses in recent weeks to the New York Jets and New England Patriots, Washington hopes its first December win of the season might come Sunday against the New York Giants.

“I don’t really have answers why it’s happening or what’s happening,” said safety Reed Doughty, who has been with the Redskins since 2006. “I know we’re going to go out each and every week to challenge them and play hard. We just need to find a way to win.”

Playing football in December is different than playing early in the season, for a variety of reasons, said Redskins Coach Mike Shanahan.

“First of all, you’ve got to have a little depth on your football team, so if you do have injuries, you stay at a certain level,” Shanahan said Monday.

The roster churn has had a significant impact on this year’s Redskins. Seven players are on injured reserve, including four starters, and two more starters are suspended for the remainder of the season. The current 53-man roster features seven players who weren’t on the Week 1 roster.

Players who are still able to take the field on Sundays often are in considerable pain from aches and bruises that didn’t exist in September.

“Everybody deals with that,” said special teams captain Lorenzo Alexander. “But also, there’s the mental part of the game — being in this facility so long from June until now. That mentally wears on you. Everyone in the league has to deal with it. It’s all about who copes with it the best and who’s able to push through and come out on top on Sundays.”

For the Redskins, the physical and mental toll has resulted in a team that relies more on rookies and less experienced players each week. Four rookies, in fact, started in Sunday’s 34-27 loss to New England — guard Maurice Hurt, running back Roy Helu, linebacker Ryan Kerrigan and safety DeJon Gomes. A fifth, left tackle Willie Smith, played the majority of the game.

Those players are asked to step up at a time of the year when they’re usually packing up their football gear. During his high school and college career, Kerrigan never had to play more than 13 games in a single year. Counting preseason games, Sunday’s game at the Giants will be his 17th in the past four months.

“Honestly, physically, I don’t feel that bad,” he said. “I feel like I’ve done a pretty good job taking care of myself, eating right, getting good sleep at night, staying active in the weight room to help sustain my legs throughout the season. It is a long season. Right now is the crunch time where you really have to take care of yourself even more.”

Not only is Kerrigan still standing, he has played every defensive snap this season — nearly 800 in all — more than any teammate on either side of the ball.

“Coach [Lou] Spanos when I first got drafted here said . . . there’s no tapping your helmet and saying, ‘I’m tired, I want to come out,’ ” Kerrigan said. “I really took that to heart.”

Statistically, recent Redskins teams have suffered major declines as the season has worn on. The Redskins last made the playoffs in the 2007 season, Gibbs’s last year with the organization. In the three-plus seasons since, they’ve tallied fewer yards in the final month of the season than in each of the first three — and they’ve averaged fewer than 18 points in their 16 post-Dec. 1 games. That ranks them 27th in the league.

Since 2007, they are ranked 14th overall in total defense but 24th after Dec. 1. The defensive units have allowed 21.3 points per game since 2008, which is 13th in the league. But once December rolls around, they give up 24.3 points per game, 25th in the NFL.

This season, the team’s stalwart pass rushers have been less effective in recent weeks. Through the first 11 games, the Redskins averaged three sacks an outing. But Washington’s pass rushers had none against the Jets and only got to the Patriots’ Tom Brady once on Sunday. Neither Kerrigan nor third-year linebacker Brian Orakpo has posted a sack since Nov. 27.

Shanahan also said momentum is important for late-season victories. A team can’t struggle early and expect to learn what it takes to pull out wins in December, when playoff hopes live and die week to week.

“You get used to winning — you know how to win,” Shanahan said. “To me, the great organizations, the great teams know how to do that, even when they do lose players.”

Staff writer Barry Svrluga contributed to this report.