As NFL’s best receiver coming out of backfield, Lions RB Theo Riddick presents Saints defense with another challenge Monday _lowres

Detroit Lions running back Theo Riddick, left, runs with the ball as St. Louis Rams defensive tackle Michael Brockers gives chase during the fourth quarter of an NFL football game Sunday, Dec. 13, 2015, in St. Louis. (AP Photo/Tom Gannam)

Calvin Johnson and Golden Tate draw the spotlight in the Detroit Lions offense.

But Matthew Stafford has another weapon, one ideally suited to give the New Orleans Saints headaches when the teams meet Monday night.

Backup running back Theo Riddick has blossomed into the NFL’s most effective receiving back this season, leading the league’s running backs with 67 catches, 578 yards and three receiving touchdowns.

“I don’t know that I’ve seen anybody this year with his exceptional quickness and really his route quickness, being able to get in and out of cuts,” Saints defensive coordinator Dennis Allen said. “It really does create a significant challenge for us.”

Contrary to popular belief, the Saints’ much-maligned pass defense has held up pretty well against wide receivers.

New Orleans has given up 1,980 yards to receivers, which ranks 12th in the NFL. The reason the Saints have allowed opponents to post a 114.2 quarterback rating — on pace to be the worst in history — has been the defense’s inability to slow down the quarterbacks’ other options.

The Saints’ issues covering tight ends have been well-documented. New Orleans has given up 1,063 yards to tight ends; the Saints are the only team in the NFL to allow more than 1,000 yards to the position.

But New Orleans has been just as bad against running backs. Only St. Louis has given up more receiving yards to running backs, and the Rams have played one more game by virtue of a Thursday night appearance this week. The Saints have allowed running backs to pick up 756 yards and five touchdowns on 76 catches.

Now the Saints face Riddick.

“I see a guy that’s really an exceptional space athlete,” Allen said. “When you watch what they try to do with him, they try to, as much as possible, get him in space situations, get him in matchups against linebackers and at times safeties. They’ll bring him out of the backfield in the passing game; they’ll line him up empty in the passing game; they’ll turn around and hand the ball to him from spread-out formations. ... This guy creates big, explosive plays for their offense.”

Riddick keeps getting good matchups in part because the Lions have so many other weapons. A defense can’t commit a nickelback to Riddick because of the presence of Johnson, Tate and tight end Eric Ebron, among others.

By virtue of his position, Riddick also ensures chances to catch the ball as a check-down option. With any receiving back, the key isn’t so much keeping the ball out of his hands as it is to make the tackle in the open field.

And on top of that, Riddick has made himself into an exceptional route-runner. For the Lions, the third-year back has essentially been Detroit’s No. 3 receiver.

“I think he’s a great weapon,” Saints head coach Sean Payton said. “When you watch him, and his route-running tree, and his ability to create problems on linebackers, it really stresses your coverage principles.”

New Orleans will have its work cut out this week. Tampa Bay’s Charles Sims, another talented receiving back, led the Buccaneers with six catches last week and got free down the sideline on a play that might have been a touchdown if Jameis Winston had made a good throw.

Linebackers Dannell Ellerbe and Stephone Anthony, safety Kenny Vaccaro and nickelback Kyle Wilson likely all will get chances to stop Riddick.

“He looks like he’s making guys miss. He’s a hard guy to tackle in open space,” Ellerbe said. “You’ve got to bracket him; you’ve got to double him; you’ve got to hit him; you’ve got to put your hands on him. You’ve got to do whatever you’ve got to do.”