The Washington Redskins, by most measures, have one of the NFL’s most productive offenses this season. They have moved the ball, put points on the scoreboard and are ranked in the top 10 in many of the sport’s most significant offensive categories.

But they are last in the league at converting third downs into first downs. There is no obvious reason for the offense’s one glaring deficiency this season under prized rookie quarterback Robert Griffin III. Some in the locker room at Redskins Park say they don’t quite understand it.

“It’s just kind of a guy here and there dropping a responsibility,” guard Kory Lichtensteiger said Thursday. “We seem to move the ball so well and we’ve racked up good yardage, good numbers. It’s just a point of emphasis for us. It seems like maybe last year we struggled with this, too. I think it’ll come. It’s just you’ve got to make a play when your number’s called.”

The Redskins have managed first downs on only 14 of their 60 third-down chances this season, a 23.3 percent conversion percentage that is the league’s lowest.

The Tampa Bay Buccaneers actually have one fewer third-down conversion, with 13. But that’s in just 51 tries, so their 25.5 percent conversion percentage is 30th in the league. The Cincinnati Bengals are 31st at 24.6 percent. The league-wide average is 38.3 percent.

“We’re just having a couple key drops, a couple missed assignments,” Redskins fullback Darrel Young said. “We just have to get better from that standpoint. We say it every year. It has to happen sometime.”

The Redskins rank fourth in the league in rushing offense, seventh in total offense and eighth in scoring offense. They’re averaging 400.6 yards and 28 points per game. So it’s not a matter of being an offense that simply isn’t very good.

And yet their efficient unit grinds to a halt on third downs. The Redskins were particularly poor on that down in last Sunday’s loss to the Atlanta Falcons at FedEx Field, when they went one for nine.

“I know we didn’t do very well last week,” guard Chris Chester said. “It’s just execution. We just need to clean up our execution.”

The Redskins seem to have the offensive elements to succeed on third downs. They have a quarterback, in Griffin, who can run and throw skillfully. They have a dependable runner in rookie tailback Alfred Morris. They have a pass-catching threat at tight end in Fred Davis. They moved veteran wideout Santana Moss into their third receiver role this season, having him operate out of the slot regularly in third-down situations.

But Griffin, the NFL’s fifth-rated passer overall, with a 101.0 rating, is only 13th in third-down passing, with a passer rating of 86.6 in those situations. The Redskins don’t have any of the league’s top 49 third-down receivers. Davis is tied for 50th, with five catches.

Griffin accepted a share of the blame this week.

“If it’s third and one, you have to get one yard,” Griffin said during his weekly news conference Wednesday. “If it’s third and nine or third and 12, you have to be able to get the ball to your play-makers and allow them to make plays. Whether that’s throwing the right ball, catching the passes that are thrown or it’s getting the calls out there, it’s not one issue. In the past game, we had a couple drops and then there’s plays out there that I could’ve thrown a better ball.”

Offensive coordinator Kyle Shanahan pointed Thursday to the Redskins dropping a pair of third-down passes and being stopped on a pair of third-and-short running plays against the Falcons.

“That’s four right there that takes you to 50 percent if you make them,” Shanahan said. “So we’ve got to make those plays.”

Young said the Redskins must put themselves into better third-down circumstances.

“We’re getting in the wrong situations on third down,” Young said. “The great teams get into third and threes, third and two. We’re getting third and nine, third and 10. That’s a whole different play call. It’s a little frustrating, a little mind-boggling, just because you put so much time into third down [in practice] during the week and you don’t execute. We have to start executing.”