Jamin Davis, the Washington Football Team’s first-round draft pick and a coveted new member of the defense, was welcomed to the NFL by Matt Feiler, a 6-foot-6, 330-pound guard who made the rookie’s powerful frame appear powerless — frail, even.

It was Davis’s first defensive snap, coming with a little more than 13 minutes remaining in Washington’s loss to the Los Angeles Chargers on Sept. 12. Davis lined up at middle linebacker and shifted from just off Feiler’s inside shoulder to squarely in front of him after the Chargers sent a player in motion. When running back Larry Rountree III took the handoff and cut left, Davis followed but never saw the hulking Feiler waiting for him.

Davis, who is 6-3 and 234 pounds, bounced off Fieler like a ping-pong ball and watched the rest of the play from his back.

“I got put on my butt,” Davis said Tuesday. “My alignment was completely wrong, and the way I reacted, it just wasn’t my kind of ball at all.”

For Davis, and for many of his fellow rookie teammates, the start of his NFL career has been a mix of trial and potential, all of which was expected, Coach Ron Rivera said. Washington set out to rebuild and, ahead of Year 2, emphasized speed and youth to create a foundation and continuity. Washington wants players it can mold and retain for not just a year but for three — if not more.

But the learning curve can be steep for rookies asked to play key roles that differ from those they handled in college. As Washington’s middle linebacker, Davis has to get acclimated quickly to a more complex system and a faster tempo and also understand the roles of everyone on defense. It’s his job, as the “quarterback” of the defense, to get his teammates — and himself — properly aligned.

“You definitely have to be confident, but as far as being a ’backer, you got to know everything,” said inside linebacker Brandon Marshall, who played under Washington defensive coordinator Jack Del Rio in Denver. “You got to know your stuff. If you’re unsure of yourself out there, it’s going to show.”

Marshall played weakside linebacker under Del Rio before shifting to the middle in Wade Phillips’s version of the 3-4 defense. The scheme differed, but the responsibilities of the position remained significant.

“If I’m a corner, they tell me cover-three, cover-two, cover-one or some type of zone — all right, cool; I know what to do,” said Marshall, a free agent who considers Del Rio’s defense to be among the most complicated he was part of during his seven seasons in the NFL. “At linebacker, you got to get everybody lined up, then you have to find the open gap or the two open gaps. I have to know if it’s cover-two, and I might have to two-gap it and hit the ‘A,’ then fall back to the ‘B.’ If it’s man coverage, I know I got this back out of the backfield. I think it’s pretty tough from a mental standpoint, but if you’re on your stuff, then you’ll be fine.”

Davis’s role is similar to the one he played at the University of Kentucky. But different schemes call for different techniques, and the competition and speed of the pro game are incomparable to what he saw in college.

By Week 2′s win over the New York Giants, Davis appeared more settled in, but his playing time declined.

“He’s getting a little bit more comfortable, a little bit better feel,” Rivera said. “You could see him really starting to flow and understanding those things. He’s going to make mistakes, and that’s what rookies do. It was a nice, vast improvement to last week.”

Sam Cosmi, Washington’s second-round pick and its starting right tackle, has experienced a similar start to his pro career. But he said his “Welcome to the NFL” moment arrived a bit earlier — courtesy of Montez Sweat and Chase Young, Washington’s edge-rushing duo who tested him daily during training camp.

Cosmi has the highest run-blocking win rate of any offensive tackle in the league, according to ESPN. But his regular season debut exposed his shortcomings in the passing game. Facing the Chargers’ Joey Bosa, the 2016 defensive rookie of the year, Cosmi struggled to keep his quarterbacks clean, allowing four pressures, including a sack, according to Pro Football Focus.

Rivera said after the loss that Cosmi appeared anxious and that bad habits from his college days at Texas resurfaced.

“One of the things I was trying to work on was getting my head out of blocks and really timing up my punch and a faster kick,” Cosmi said Tuesday. “Sometimes when you try to break a habit, it takes a lot of repetition. ... I found myself doing some of that [against the Chargers], but I felt like I got better the next week.”

Against the Giants, Cosmi was flagged for two penalties — an unnecessary roughness call that hampered a second-quarter drive and a holding penalty in the third quarter that might have cost his team four points. Washington settled for a 49-yard field goal after being knocked back 10 yards on Cosmi’s third-down penalty. Yet his run blocking remained stout and he didn’t allow any pressures, per PFF.

Washington’s third-round picks, cornerback Benjamin St-Juste and wide receiver Dyami Brown, have been unofficial starters because of scheme and injuries. Washington, like many teams, plays the majority of its defensive snaps in subpackages, with St-Juste at cornerback. The Chargers tried to capitalize on his inexperience by repeatedly targeting him in coverage, and it generally worked; according to PFF, he allowed seven catches for 94 yards and a touchdown. But by Week 2, he gave up only two catches for 25 yards and had a pass breakup.

The speedy Brown has played the second-most snaps of Washington’s wide receivers, behind only Terry McLaurin. His debut included only one catch for a loss of two yards, but he also drew a pass interference penalty that set up Washington’s second field goal.

“I think he’s just going to continue to develop as the season goes on and he gets more comfortable out there,” McLaurin said. “... I think he’s going to continue to be in favorable matchups and be in situations where he can win one-on-one situations. I feel like that’s why he’s here.”

Washington has its first road game Sunday at Buffalo, where undrafted rookie running back Jaret Patterson made his name as a college star. With Washington, his opportunity has been minimal; he has been on the field for only four offensive plays (all against the Chargers) and has just two carries for nine yards. That’s a stark change from his time at the University at Buffalo, where he ran the ball 141 times in six games during his final season.

But Patterson said this is nothing new to him.

“I feel like this is deja vu for me,” he said. “I had to grayshirt, and when I got there my freshman year, I had to kind of wait my turn. ... You have to be ready when your opportunity presents itself, which I know it will.”

Like Davis, who was on the field for 39 percent of the defensive snaps in Week 2 after playing 56 percent in the opener, Patterson said he has taken mental reps on the sideline, envisioning himself in the position of Antonio Gibson or J.D. McKissic. But that can’t replicate on-field experience.

Rivera is of the mind that a player doesn’t fully learn a system or become comfortable in his role until he has had 5,000 game reps. That means Washington’s rookies have only just begun.

“The only thing that builds experience, obviously, is doing it,” Rivera said. “... The more and more reps you get, the better you’re going to become.”