Redskins defensive coordinator Joe Barry, here instructing Trent Murphy and Jackson Jeffcoat last season, likens his job to a teacher’s when a math student is getting poor grades. “You could say, ‘Oh, that kid is just dumb.’ Well, I look at it as: The teacher is not getting it out of him.” (John McDonnell/The Washington Post)

With their defense mired at or near the bottom of several significant statistical categories, the Washington Redskins made four roster moves this week designed to upgrade their performance. But defensive coordinator Joe Barry acknowledged Thursday that he had to do a better job coaching the players on hand.

Asked how he felt he was doing in terms of getting the most out the defense, Barry said, “Well, not good. A job of a coach is no different [than] a teacher. And if a math student simply isn’t just getting the good grades on math tests, you could say, ‘Oh, that kid is just dumb.’ Well, I look at it as: The teacher is not getting it out of him.

“I put a lot of pride and a lot of input on myself to get it done, and we’re not getting it done right now. I’m not getting it done.”

Second-half takeaways sealed Sunday’s victory over the Cleveland Browns, which lifted the Redskins to 2-2. But the game highlighted two glaring defensive weaknesses — tackling and third-down stands. The Redskins rank 31st in rushing yards allowed per play (4.88) and 32nd in third-down defense (57.5 percent).

Inside linebacker Will Compton, right, says he looks at what he can do to improve the Redskins tackling before pointing fingers elsewhere. Washington is among the league’s worst rushing and third-down defenses. (Carolyn Kaster/Associated Press)

Against the Browns, the defense fared even worse than its season averages, missing more than a dozen tackles, by Coach Jay Gruden’s count, which helped running back Isaiah Crowell gain 7.5 yards per carry.

Asked how the tackling could be so poor four games into the season, Barry said there was no single answer, noting that the Redskins have missed tackles at the line of scrimmage, tackles in space, head-on tackles and tackles at an angle. “It’s not one clear, clean specific tackle that we say, ‘Hey if we clean this up, we’re good,’ ” Barry said. “It’s really across the board, and it’s been frustrating.”

The Redskins also allowed rookie quarterback Cody Kessler to convert 67 percent (eight of 12) of the Browns’ third downs. Barry said it boiled down to one-on-one matchups.

“That’s what tackling is all about, and that’s what third downs are all about — winning that one-on-one matchup — and we have not consistently done that,” Barry said.

Gruden acknowledged Thursday that statistically the defense hasn’t been “as good as we would like.” But he pointed to its strong second halves in the past two games, shutting out the New York Giants and holding the Browns to three points.

Still, it’s imperative the defense improves, said Gruden, who hired Barry, then San Diego’s linebackers coach, to succeed defensive coordinator Jim Haslett in January 2015.

Asked whether he felt Barry was getting the job done — in terms of strategy, midgame adjustments and teaching tackling fundamentals — Gruden said he felt “fine” about it. “That’s something we address at the end of the season,” Gruden added. “Right now, we’re in good shape. We haven’t played up to our standard, without question. . . . We played well in the second half in both games, both our victories, and we’re creating turnovers. That’s good. There’s positives to be had.

“Now our tackling hasn’t been on par for what we demand around here. That’s something we can improve on, and maybe there are some issues that we can work on fundamentally, and there’s maybe some schematic things that we can work on.”

On Wednesday, Redskins General Manager Scot McCloughan released defensive lineman Kendall Reyes, a free agent acquisition who had appeared in just two games, and put safety David Bruton Jr., who missed more than his share of tackles before suffering a concussion, on injured reserve.

McCloughan used the roster spots to bring in two new safeties: Donte Whitner, a three-time Pro Bowl honoree, and Josh Evans. Gruden characterized both as “question marks” Thursday; coaches are still trying to determine what sort of shape Whitner, 31, is in and how quickly Evans, a fourth-year player, can pick up the Redskins’ defensive system.

The roster moves seemed to suggest that the defense’s shortcomings are matters of personnel rather than coaching.

Inside linebacker Will Compton said that’s the only way players should view it.

“As players, if you’re going to be successful, you have to be accountable; you can’t be pointing the finger,” said Compton, a defensive co-captain. “I see it all as my fault. I feel like that’s how everybody needs to handle that situation. ‘How can I play better in my technique? How can I help this tackle out over here? How can I make it easier on [fellow linebacker] Mason [Foster]? This safety?’ ”

Compton said no extra time has been set aside in practice for tackling drills this week but that coaches are emphasizing swarming to the ball, getting good body position for maximum leverage against ball-carriers and being more violent against the run.

In Barry’s view, it is a “two-way street.”

“You know, obviously, players have got to play and make plays on the field. But as a coach, I’ve got to get us to win on third down better,” Barry said.

“I’ll turn over every rock to get what the issues is solved because that’s my job as a coach. That’s my job as a teacher. And I promise you, it was worked on yesterday in practice; it’ll be worked on today at practice until we get it solved.”