Linebacker Trent Murphy, left, guard Spencer Long and other Redskins have been taking their aggressions out on each other for the first 11 days of training camp. Day 12 brings the New England Patriots. (Alex Brandon/Associated Press)

Since suiting up for training camp July 23, the Washington Redskins have practiced in shells and in full pads. They’ve held walkthroughs and collided in live drills. They’ve worked on fundamentals and practice plays scripted for the red zone. They’ve squared off one-on-one, seven-on-seven and 11-on-11.

Now comes an opponent that’s more authentic than a tackling sled and quicker to rile up competitive fires than a teammate.

Coach Jay Gruden’s hope is that three days of joint practice with the New England Patriots heading into the teams’ preseason opener Thursday at FedEx Field will challenge his players anew and give his coaching staff another means of judging who’s worthy of a spot on the 53-man roster.

Take Redskins offensive line coach Chris Foerster. While his starting five is fairly well set, Foerster has a glut of linemen jockeying for backup spots. With fewer than four weeks before the final cuts must be made, it’s unclear whether Gruden will end up keeping eight offensive linemen or 10. Either way, Foerster must identify the contenders who are both the most promising and versatile.

“When you bring a different color jersey in, the intensity level automatically steps up a little bit,” said Foerster, an enthusiastic proponent of the joint practices that will be held Monday through Wednesday at the Redskins’ Richmond training camp.

“Now, it’s nowhere near the preseason game [in terms of intensity], which is nowhere near the regular season. And it’s nothing like the playoffs. But it just paints a broader picture. You get a better evaluation of your players. Now, all the sudden, you’ve got to block a silver helmet and not a burgundy.”

It’s not the first time the Redskins have squared off against another team during training camp. The Pittsburgh Steelers served as their mid-camp measuring stick in the 1980s and ’90s, with the teams holding annual scrimmages that alternated between the Steelers’ Latrobe, Pa., base and the Redskins’ camp in Frostburg, Md., or Carlisle, Pa.

But this is the first time the Redskins have scheduled a multi-day joint workout, as the Cincinnati Bengals and Atlanta Falcons held last season and the Baltimore Ravens and San Francisco 49ers will following their preseason opener.

“You have limited numbers in camp,” NFL Network analyst and former Redskins general manager Charley Casserly said, “so you get more reps for your players because you’re not hitting yourself.”

It also helps break up the sheer monotony of camp, in which NFL players practice twice a day, six days a week for roughly three weeks, as well as study film and attend meetings in the evening.

Some coaches also have strategic reasons for pitting their squads against specific opponents.

“If you’re a 4-3 [defensive-schemed] team and you’re going to play a bunch of 3-4 defenses, you may want to practice against a 3-4 team,” Casserly said.

The Post Sports Live crew explains why no major news out of training camp is good for the Redskins coming off of a 3-13 season. (Post Sports Live/The Washington Post)

In the Patriots, the Redskins’ defense will get to test itself against one of the league’s more explosive offenses. In his 13 seasons as New England’s starting quarterback, Tom Brady has led the Patriots to three Super Bowl championships, compiled a 95.7 career passer rating and earned nine Pro Bowl honors. No NFL quarterback has started more playoff games (26) or won more (18) than Brady, who turned 37 on Sunday.

New England’s defense is less imposing — 18th against the pass and 30th against the run last season — but the team used its No. 1 pick in this year’s college draft to acquire Florida defensive tackle Dominique Easley and signed cornerback Darrelle Revis in free agency.

Redskins Pro Bowl running back Alfred Morris relishes the test in store.

As Morris explains, during typical training-camp practices, the offense knows what its own defense is going to show, and the defense knows how the offense plans to attack.

“We know, ‘Oh, it’s a blitz period! Oh, it’s a run period!’ So you kind of expect it,” Morris said last week. “But going against another team, it gives you a different level of competition. Mentally, it changes our psyche. It just makes you want to work that much harder because you’re going against a real opponent, not your own teammates.”

But not everybody sees the value.

“I’m not a fan of that, to be honest with you,” said cornerback Cary Williams, whose Philadelphia Eagles held joint practices with the Patriots last preseason.

“I don’t see why we’ve got to go three and four days with those guys if we’re going to play them on the fourth day. They know us. We’re going to know them. I like the mystery. I used to like the mystery. You just come into camp. You do your camp. You go against those other guys, and you get that itch to go hit some other guy. When you practice against other guys, other teams early on, you don’t get that itch. That itch is gone.”

On a broader scale, the joint workouts will give the Redskins’ coaches and front office a first-hand look at the work habits of an NFL franchise that since 2000 has served as a model of stability and success.

Bill Belichick has been New England’s coach since 2000. In that time, his Patriots teams have posted a 163-61 record (.728) and won three Super Bowls and five AFC championships.

As Gruden put it, working alongside and against the Patriots will give his young Redskins a chance to state their case for roster spots against an NFL team that has been good for a long time.

Mark Maske contributed to this story.