The Post Sports Live crew discusses some of the highlights and lowlights from the 2012 season for the Redskins’ defense. (The Washington Post)

When Coach Mike Shanahan and his staff break down the Washington Redskins’ defense this offseason, they will examine a unit that stumbled out of the gate before making strides down the stretch — and one with pressing needs that still must be addressed before next season.

Originally projected as a strength of a team that was expected to endure a rookie quarterback’s offensive growing pains, the defense was anything but formidable during the first half of the season.

The early struggles began with season-ending injuries in Week 2 to top pass rusher Brian Orakpo and one of the team’s top run-stoppers, defensive end Adam Carriker , who also had 5.5 sacks in 2011. Strong safety Brandon Meriweather battled knee injuries and wound up playing only half a game before he tore his ACL in Week 11. And projected starting free safety Tanard Jackson was suspended for the year for violating NFL substance abuse policies.

“In the beginning it [was] hard,” defensive coordinator Jim Haslett recalled. “You lose two safeties who I think are two really good football players, and in the matter of five plays you lose your best pass rusher and your best defensive run player on the front. So, it’s not easy.”

Without Orakpo, Haslett was forced to platoon of Rob Jackson and Chris Wilson at the right outside linebacker position. He turned to second-year pro Jarvis Jenkins — who missed all of his rookie season with a torn ACL — to replace Carriker. In the secondary, Madieu Williams and DeJon Gomes started the year at free and strong safety, respectively. But soon, Haslett replaced Wilson with special teams ace Lorenzo Alexander, and Gomes with Reed Doughty.

The Washington Post’s LaVar Arrington, Dan Steinberg, Jason Reid and Jonathan Forsythe peer into their collective crystal balls to offer their bold predictions for the Redskins in 2013. (The Washington Post)

The result was not an immediate turnaround, however. The Redskins struggled to get to the quarterback and the secondary was susceptible to the big play.

As Washington entered the bye with a 3-6 record, the defense ranked 30th in the league, giving up 397.9 yards per game, including 301.7 yards through the air. The unit gave up 27.6 points per game, fifth most in the league. Big gains by opponents proved crippling; in their first nine games, the Redskins yielded 17 pass plays of 25 yards or more.

Haslett came back from the bye determined to get more out of his unit than he had in the first half of the season. Because an in-season talent overhaul wasn’t possible, and with no healthy player versatile enough to play strong safety full-time, Haslett shuttled Doughty, Gomes and Jordan Pugh in and out of the lineup, depending on the situation. On most run plays, Doughty got the nod, On some pass plays, Pugh came in, on others it was Gomes. Together, they began to get the job done.

To help his pass rush, Haslett concocted ever more exotic blitzes. He’d overload the edge, with inside linebacker Perry Riley coming from the outside as well. At other times, he’d send left outside linebacker Ryan Kerrigan on a stunt up the middle. Haslett also gave Jackson more opportunities on third down, and the linebacker delivered with 4.5 sacks in the second half of the season.

Meanwhile, defensive linemen Barry Cofield and Stephen Bowen — playing in the system for a second straight season after signing as free agents in 2011 — began making plays.

“It’s everything,” Haslett said of the options he and his coaches considered. “We talk about it and say, ‘Let’s try this guy and this. Can Rob Jackson be a full-time player? Can Lorenzo be a full-time player? Can Chris Wilson?’ We want to throw all of the combinations out there and you try to figure out what they do best.”

Defensive players started describing Haslett as “a mad scientist” and “chess master,” as his tinkering yielded results. In the seven games that followed the bye, Washington allowed 351 yards a game (270 passing) and limited opponents to 20.1 points per game.

The unit’s inability to get stops returned in the playoffs against the Seattle Seahawks, who rallied from 14 points down to earn the victory. But despite their disappointment, the Redskins draw encouragement from their second-half showing.

“We have a lot to build on,” Bowen said. “All the guys that stepped up in the season regardless of injury, we’ve been playing a lot better, and we’ll have a lot more depth on defense.”

The returns of Orakpo and Carriker should help next season, but fixing the secondary remains a top priority.

Meriweather remains under contract, but the Redskins won’t know what kind of recovery he can make until later this spring or summer. Williams, Jackson and cornerback Cedric Griffin are free agents, and cornerback DeAngelo Hall — despite a strong finish to the season — faces an uncertain future because he carries a $7.5 million cap hit next season. Captain London Fletcher, the heart of the defense, is taking some time to decide whether to return next year.

“You look back at it at the end of the year when it’s over and you try to analyze what you did well and what you didn’t do well and you try to fix it,” Haslett said. “Then you take that into next year. . . . Now you just have to try and build off of it every year. You have to try and keep adding to it and getting better.”