Washington Redskins quarterback Kirk Cousins passes against the Philadelphia Eagles at Lincoln Financial Field on December 26 in Philadelphia.

Washington Redskins quarterback Kirk Cousins passes against the Philadelphia Eagles at Lincoln Financial Field on December 26 in Philadelphia. Toni L. Sandys/The Washington Post

Standing in the visitors’ locker room at Philadelphia’s Lincoln Financial Field the day after Christmas, Redskins Coach Jay Gruden took in a chaotic scene as he and his players tried to make sense of one of the oddest endings to a first half that anyone had ever witnessed.

With a chance to take a double-digit halftime lead over the Eagles with the NFC East crown on the line, Washington’s offense had marched downfield in 29 seconds, reaching the 6-yard line with six seconds remaining and no timeouts left. The Eagles inexplicably did the Redskins a favor, calling timeout.

That should have set up Washington to plan for a quick shot to the end zone. If that failed, there would still be time for a field goal attempt.

[D.C. Sports Bog: Mel Kiper doesn’t like Redskins’ playoff chances]

But quarterback Kirk Cousins took the snap, then took a knee, running out the clock. After the game, Cousins said he’d had “a lapse in his decision-making.”

The Washington Post's Gene Wang discuss the Redskins' division-clinching win over the Philadelphia Eagles. (Thomas Johnson,Randolph Smith/The Washington Post)

In the locker room, wide receivers Pierre Garcon and DeSean Jackson interrogated Cousins, then Gruden. Defensive players grilled offensive players for details on the play call in the huddle. Offensive players pumped their coaches for clarity.

“Halftime was, uh, pretty crazy,” Gruden said with a chuckle five days later, sitting on a couch outside of the weight room at Redskins Park. “Really crazy, to be honest with you. To be up 16-10 on the road to win a division, you would’ve thought we were down 63-16. Eventually, we got them all settled down.”

After managing to silence the locker room, Gruden first took blame for the situation, saying he didn’t clearly convey to Cousins what should have happened. And then, the coach reminded his players of the score.

“ ‘Hey, we’re up 16-10, and we’ve got the ball. We’re in good shape. It’s not the end of the world,’ ” Gruden recalled telling his team. “I said, ‘People make mistakes.’ It was just that it was the quarterback, doing something you don’t normally see. But I told them, ‘Hey, we could’ve missed that field goal. Or it could’ve been blocked for a touchdown. They’ve got great special teams. Just relax.’ ”

[Five story lines for the season finale in Dallas]

The words had their intended effect. Defensive players and coaches retreated to their side of the locker room and addressed their first-half problem areas. Offensive players and coaches got on the same page for their assignments.

Some players called Gruden’s work during those moments his greatest coaching since coming to Washington. Although he conveyed poise at the time, Gruden admitted in retrospect, “I probably would’ve hitch-hiked back home if we had’ve lost that game by a point. Really.”

Neil Greenberg, The Post's resident stats guru, makes his weekly NFL picks, going head-to-head against cats from the Montgomery County Animal Services and Adoption Center, a shelter in Maryland. All cats featured in the video are available for adoption. (Thomas Johnson/The Washington Post)

The Redskins did not lose by one, and Gruden, on the team’s flight home, celebrated after a 38-24 victory that clinched the NFC East.

The night marked one of the many twists and turns during a Redskins season that opened with, at best, modest expectations and will close with a wholly unexpected trip to the playoffs. Five moments proved more significant than others.

1. Griffin down, Cousins up

Throughout the offseason and training camp, Gruden offered only support for Robert Griffin III, the No. 1 draft pick who guided the Redskins to playoffs in 2012 but whose star had fallen after injuries and the struggle to transition from a read-option offense to one based around a more traditional pocket passer.

Griffin remained erratic during training camp, and Gruden said he couldn’t ignore the fact that Cousins, who had fallen short in his five-game stint as the starter last season, was displaying great growth.

“Not that Robert failed miserably, it was just that Kirk really showed the most progress, by far,” Gruden recalled. Griffin was still the starter through the first two preseason games, but the coach was already considering turning the reins over to Cousins.

[From the archives: Gruden names Cousins starter]

“We were starting to lean that way, and then it was pretty clear the Baltimore game,” Gruden said.

In the Aug. 20 preseason game against Detroit, Griffin held on to the ball too long, failed to call out proper pass protections for the offensive line, got sacked three times, was hit thrice more and left the game with a concussion.

Cousins stepped in against Baltimore on Aug. 29 and completed 20 of 27 passes for 190 yards, a touchdown and one interception. The Ravens’ defense failed to register a sack.

The next day, Gruden informed General Manager Scot McCloughan of his plans to go with Cousins as his starter. It was important, Gruden said, for the team to pick one quarterback and stick with him; let Cousins grow through ups and downs. There would be no carousel.

McCloughan — hired in January to bring long-elusive stability to the franchise — agreed, and the two men received the blessing from team president Bruce Allen and owner Daniel Snyder during a meeting that weekend.

“I was surprised,” Cousins recalled. “People forget that up until that point, I was going with the [third-stringers] every other day. . . . [Against the Lions] I played in the fourth quarter. You play in the fourth quarter, you’re playing with undrafted free agents, guys that are fighting to make the team. . . . I remember telling my dad, ‘I’m just competing to be a backup.’ ”

Eighteen weeks later, Cousins is setting franchise records and leading his team to the playoffs.

“The proof’s in the pudding now,” center Kory Lichtensteiger said. “We’re playoff dancing because of him. [At the time of the decision], it was good to see that there’s repercussions and rewards; repercussions for not playing well and rewards for doing the right thing: preparing, performing in practice and the preseason. It was just good to know that you get rewarded for hard work and performing.”

2. First game-winning drive

The Redskins stumbled as the regular season began, going 1-2 with Cousins throwing four interceptions and only three touchdowns.

Washington entered its Week 4 home game against Philadelphia in need of a win, yet after blowing a double-digit first-half lead, the team trailed 20-16 midway through the fourth quarter.

That was when the Redskins saw Cousins come into his own, teammates say. He capped a 15-play, 90-yard drive by hitting Garcon with a four-yard score with 26 seconds remaining. The Redskins won, 23-20, to even their record at 2-2.

[From the archives: Cousins leads Redskins rally]

“Pierre had great separation on his route and I had to throw with a little bit of anticipation, and he made just an unbelievable catch,” Cousins remembered.

Garcon had made tough catches before, but it was Cousins’s poise in the situation that resonated with his teammates.

“Give Coach Gruden credit for making a hard decision, but making the right decision,” defensive end Chris Baker said after the game. “This was the game that showed you why he went to Kirk. We all love Robert, and we hate to see him not getting the chance he worked so hard for. But you see the production with Kirk, and now you see he can lead us to victory in the fourth quarter.”

3. ‘Code Red’ comeback

Following back-to-back losses to Atlanta and the New York Jets, Gruden described the Week 7 home game against Tampa Bay as “code red.” The team was about to enter its bye week, but a loss to the Buccaneers would mean a three-game losing streak with unbeaten New England waiting after the week off — and the very real possibility of hitting the season’s halfway point at 2-6.

The urgency Gruden was seeking, however, was absent as Tampa Bay took a 24-0 first-half lead. Cousins ran for an eight-yard score to cut the margin to 24-7 at halftime.

“Things seemed pretty bad,” Gruden admitted this past week.

[From the archives: Cousins-led rally stuns Bucs]

The team’s veterans went into the locker room and urged their teammates not to give up.

“You had guys like Trent Williams, Dashon Goldson, D-Hall, who were keeping everyone upbeat at halftime,” rookie safety Kyshoen Jarrett remembered. “If anything, just leave it all on that field, and we did and at the end of the day, we were able to get the win.”

Washington cut the Bucs’ lead to 24-21 in the third quarter. Then, with just more than four minutes remaining, the defense provided one of its most valiant stands of the season. The sequence started when Tampa Bay running back Doug Martin broke free up the right sideline for 49 yards. He would have scored had cornerback Bashad Breeland not caught him from behind at the 5-yard line. The Redskins then denied Tampa at the 1 and forced a field goal.

“You’re talking about plays of the season, you’ve got to talk about Breeland’s tackle,” Gruden said shaking his head. “Touchdown puts them up by 10 and puts us away.”

Instead, the Redskins were down, 30-24, when Cousins and the offense took over with 2:24 remaining. It was more than enough time for Cousins to lead his second game-winning drive, this one 11 plays and 80 yards, capped by a six-yard scoring pass to Jordan Reed. Dustin Hopkins tacked on the deciding extra point, and Washington avoided disaster.

4. First road win

The seesaw ride continued for the Redskins. They were 5-7 entering their Week 14 matchup at Chicago, still seeking their first road win. Gruden was 1-12 away from FedEx Field since taking over the Redskins in 2014.

The Redskins knew the only way for them to get into the driver’s seat of the NFC East would be to end that streak of futility. So they did what they’d been doing for months — they responded, jumping out to a 21-7 lead before weathering a third-quarter Bears comeback effort.

The defense made another late stand, and fortune smiled when Chicago’s Robbie Gould missed a 50-yard field goal that would have tied the game at 24.

[From the archives: Redskins get monkey off their backs in Chicago]

“Getting that first road win was huge because it finally got the demon off our back,” Baker said.

“That Chicago game,” Williams said, “that’s when I knew we could do something. It just felt like it put us over the hump. We hadn’t been able to win on the road, and we finally proved that we could. It did a lot for us confidence-wise.”

The 24-21 victory started a three-game winning streak that could extend to four with a win over Dallas on Sunday in the season finale.

5. The clincher

Washington could have lost at Philadelphia in Week 16 and still maintained a chance to win the division. But doing so would have meant forfeiting control over their playoff fate. Instead, the Redskins approached last weekend’s game as if a loss would eliminate them from postseason contention.

Having earned their first road win only weeks earlier, the task of winning away from FedEx Field didn’t even enter players’ minds.

“We had that confidence going in, so that’s why it was big for us to go to Chicago and win there,” Jarrett said. “We just approached [the Eagles game] like a business trip and knew we could do it.”

[From the archives: Redskins clinch NFC East, playoff spot with win]

The division-clinching win featured bits and pieces of all of the previous defining moments. Adversity returned again thanks to the confusion just before the half. But the poise and resolve developed from earlier in the year, and Gruden’s leadership skills, prevailed.

“It was the cumulative effect of the season,” Hall said. “. . . It’s been guys battling off adversity, coming off tough losses, whether a blowout in Carolina – it’s those losses, and even the wins after those losses that help define the season.”

As the clock ticked down on the 38-24 win, Gruden received his first Gatorade bath as an NFL head coach.

“It’s a great feeling, but we feel like there’s a lot more to accomplish,” he said. “It’s one thing to have Gatorade poured on you winning a division, but you’re really thinking about the other one.”

Master Tesfatsion contributed to this report.