The Washington Redskins built the sort of young defense they wanted, one with depth and talent at key areas – such as the line and secondary. That depth is being tested again. And how the Redskins respond will shape their postseason hopes.

The Redskins, if relatively healthy, are legitimate playoff contenders and a threat to win the NFC East. But they are no longer relatively healthy and have already lost one key starter for the season, rookie defensive lineman Jonathan Allen, to a Lisfranc injury.

But they’re entering a crucial game vs. Philadelphia on Monday night without, possibly, their starting cornerbacks – Josh Norman (rib) and Bashaud Breeland (knee). Perhaps one or both will play; more will be learned about that Thursday. But both might not.

The Redskins (3-2) are fortunate to have excellent depth -- and young talent -- at corner. But that depth is inexperienced. If the starters can’t play, the Skins will go with third-year player Quinton Dunbar, a converted receiver, and Fabian Moreau, a rookie. The latter could become an excellent player someday soon, and Dunbar has skills that have always been intriguing. But he has started only four games, and Moreau will be playing in his sixth.

There's a chance the Redskins will face Philadelphia on Monday with second-year cornerback Kendall Fuller, having a strong season in the slot, as their most experienced corner. There's a natural learning curve; it helps to have communicative veteran safety D.J. Swearinger, but there's only so much he can tell them during the game.

"The young guys have to do a good job learning regardless if they're third, fourth, fifth string," Swearinger said. "They have to prepare like a starter, and that will help the communication out. I take a lot on myself ... but it shouldn't be like that. It really should be we're all on the same page and the communication should be smoother."

“No excuses,” Moreau said after Sunday’s win over San Francisco.

Dunbar has continued to improve and showed it Sunday vs. the 49ers. He made some key stops in coverage, showing more awareness in coverages other than press-man. Dunbar is aggressive with jams and press coverage. Against the 49ers, he forced a wide throw by maintaining his outside leverage when the receiver cut outside. He’s not perfect, but he’s growing.

“It’s more from a motivation standpoint, like, ‘It’s your time,’” Dunbar said. “I’m 1,000 times better at understanding the offense and stuff like that. Man-to-man coverage comes easy to me. I’m fast and physical. I can play that. But the mental takes me to the next level.”

With young players come growing pains for a defense that was already undergoing a learning curve because of the new parts in the lineup. There have been a number of times through five games when two players chat after a play because one of them has blown an assignment. Those mistakes are a result of youth and not having played enough together.

The changes the Redskins made on the defensive coaching staff also are a factor. Defensive backs coach Torrian Gray, who was hired in February 2017, was known as a technician before he arrived, something the Redskins needed. While former defensive backs coach Perry Fewell focused more on the big picture, Gray goes smaller and harps on the details.

Defensive line coach Jim Tomsula, hired in January 2017, wants players with a certain mindset. There’s a reason the Redskins made moves in the offseason. But more importantly, he focuses on technique and doesn’t place limitations on a player. Tomsula rotated his players throughout camp – in practices and games. The idea was to test every player vs. the starters. That fosters development.

He’s missing two players from his original group: Allen and nose tackle Phil Taylor (lost in the preseason). But Tomsula’s approach leads to growth. Now he’ll need Ziggy Hood, Stacy McGee and Terrell McClain to do more.

First and foremost, players must help themselves. But having motivated, hardworking players with coaches such as Tomsula and Gray speeds that development. Second-year lineman Anthony Lanier II is not Allen. The latter was playing well with a mature game. He could line up at multiple spots along the front and even rushed a few times standing up, with Matt Ioannidis at nose tackle.

Having Allen and Ioannidis collapse the pocket enabled the Redskins to often rush with four and cover with seven. That’s a luxury. They’re actually using four-man rushes as often as they did last season. The difference: In 2016, opposing teams completed 69.2 percent of their passes and averaged 7.58 yards per attempt vs. that look. This year, it’s 62.7 percent and 6.71 yards per attempt, according to ESPN Stats & Information. The combination of a better pass rush and an improving secondary has made a difference.

Every team has injuries, so dealing with them is nothing new. Knowing Tomsula, his energy won’t change because he has lost one guy. At least Norman and Breeland will return at some point, so it’s not as if the defense has been depleted. The Redskins lost a talented young lineman who was making a difference. They'll need another one – Lanier – to do the same. It’s asking a lot, but the Redskins finally took the right approach to defense this offseason. Now it needs to pay off.