New Orleans Saints running back Alvin Kamara (41) celebrates his touchdown against the Philadelphia Eagles during the second half Sunday, Nov. 18, 2018, at the Mercedes-Benz Superdome in New Orleans. The Saints won 48-7.

When Alvin Kamara looks across the line of scrimmage and sees a linebacker across from him, he only has one thought.

“First down,” the New Orleans Saints running back said.

The secret has been out for a long time. Opposing teams know Kamara is one of the NFL's more versatile weapons, and they spent the year approaching him as such.

Some approaches worked. Others failed. But those who did not flex at all typically end up burned. Even teams like the Dallas Cowboys, who might have the rangiest linebackers in the league, had a cornerback spy Kamara in passing situations when the teams met Nov. 29 in a 13-10 Dallas win.

This week's opponent in the NFC divisional playoffs, the Philadelphia Eagles, even double-teamed Kamara at times when the teams played Nov. 18, a 48-7 blowout win for the Saints.

If someone doesn't want to go that far, teams must answer one question: Do you keep a linebacker on the field against Kamara in case it is a running play, or do you put an extra defensive back out there to cover his receiving ability?

Neither decision is ideal.

“You’re going to get a safety or a nickel over him because the threat he is running routes and catching the ball down the field,” running back Mark Ingram said. “They put a linebacker on him, and we’re going at them. They’re not going to be able to cover him. Nickels and safeties even have a hard time covering him.”

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Ingram isn’t wrong. After reviewing all of the Saints passing plays from the regular season, The Advocate determined Kamara ran 317 routes. He was covered by a defensive back on 149 of those plays.

That seems like a significant number for a running back — but it's not surprising, given that 114 of those routes came when he split out like a wide receiver. On all but 18 of those snaps, a defensive back covered Kamara.

In a lot of those instances, the personnel dictated the coverage. What’s more revealing is that teams respected Kamara's ability out the backfield enough to keep a defensive back on him 57 different times throughout the season. The Falcons and Cowboys were among the those most committed to this approach.

It’s probably not a bad idea.

The running back was targeted 55 times with a linebacker in coverage, and he made 44 catches for 322 yards. Kamara can run by them and cause damage, but the flip side is he still had 13 receptions for 125 yards when a defensive back covered him out of the backfield.

Keeping a safety on Kamara comes with other drawbacks. That coverage means some other Saints player is likely to end up getting a better matchup because of it.

One example came in a Week 4 game against the Giants when a safety stayed with Kamara, which allowed tight end Ben Watson to run by a safety on a corner route for a gain of 23. Another one came in Week 16 when the Pittsburgh Steelers chose to double the running back on a route to the flat, which allowed Keith Kirkwood to run free for a gain of 23 yards.

The other players are more than willing to accept the advantageous looks.

“Defenses can only deal with so much. It gives you options,” Watson said. “Those two players (Michael Thomas and Kamara) are the bulk of our passing offense, and the bulk of who we target and who we draw plays up for and try to get open. They may come into a game thinking they have to stop those two guys, but it doesn’t mean you can actually stop them.”

The Philadelphia Eagles had safety Malcolm Jenkins cover Kamara for most of the game when he lined up like a wide receiver when the teams first met earlier this season. But sometimes Jenkins was joined by another player.

The Eagles felt it necessary to double-team the running back several times, which backfired when it opened up the field for others to make plays. Kamara only had one catch for a 37-yard touchdown, but he deserves credit for creating so much more offense.

Jenkins and linebacker Jordan Hicks doubled Kamara on a 23-yard gain by Dan Arnold and a 38-yard reception to Smith. The Eagles were also paying heavy attention to Thomas on both plays, which left everyone else on the field in favorable matchups.

On another play, Hicks and Nigel Bradham doubled Kamara on a route to the flat. With the linebackers removed from the middle of the field, it created an easy 22-yard reception for Smith.

It seems obvious, but how much does Kamara’s presence impact the game? And how much has he grown from last year, when he was just a rookie?

“A lot,” quarterback Drew Brees said. “I don’t know how his numbers compare from last year to this year, but he’s reliable, and I know what he’s going to do. We ask him to do a lot. Do a lot from the backfield, do a lot splitting him out, putting him in motion — different things. His versatility’s really valuable. I feel like his route tree’s broadened from last year to this year.”

It’s true that Kamara’s numbers are a little down. He caught the same amount of passes each of the past two seasons, but he finished last year with 826 yards compared to 709 this year. Part of that is because the Saints' screen game struggling a little this season, and another factor is the attention that Kamara receives.

Kamara could become frustrated by it, but he chooses not to. He likes it when a defense focuses on him.

“I think that’s just a sign of respect,” he said.

It certainly is.

Follow Nick Underhill on Twitter, @nick_underhill.​