RICHMOND, Va. — Since suiting up for training camp July 23, the Washington Redskins have practiced in shells and in full pads. They've held walk-throughs 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 more authentic than a tackling sled and quicker to stoke 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 while giving his coaching staff another means of judging who's worth keeping on the 53-man roster.

Take Redskins offensive line coach Chris Foerster. While his starting five is fairly set, Foerster has a glut of linemen jockeying for backup spots. With less than four weeks before final cuts, it's unclear whether Gruden will end up keeping eight offensive linemen or 10. Either way, Foerster must identify the contenders.

"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 today through Wednesday at the Redskins' training camp in Richmond.

"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."

Explained former Redskins general manager Charley Casserly, now an NFL Network analyst: "You have limited numbers in camp, so you get more reps for your players because you're not hitting yourself."

It also helps break up the monotony of camp, in which NFL players practice twice a day, six days a week, for roughly three weeks, in addition to studying film and attending meetings in the evening.

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

"If you're a 4-3 [defensive] 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.

With 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, which largely explains why the team used its first-round pick in this year's draft to acquire Florida defensive tackle Dominique Easley.

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."