There are two David Onyematas on the New Orleans Saints' roster.

There's locker-room Onyemata.

And there's gameday Onyemata.

Locker-room Onyemata is one of the quietest guys around, typically sitting at his locker, scrolling through his cell phone while more outspoken defensive linemen answer reporters' questions.

But then there's the other Onyemata.

"When people talk about turning on a switch, there are a couple switches for him," defensive tackle Taylor Stallworth said. "And he turns all of them on for game day. It's funny because you don't expect that. The first time I heard him trash-talk in a game I was like, 'Oh my.’ ”

Stallworth says some of Onyemata's trash talk isn't suitable for publication. But some of it is.

Rookie defensive end Marcus Davenport recalls a common phrase Onyemata uses.

"He's strong, and when he hits somebody, he always yells, 'Do better! I need more!’ ” Davenport said. "It's funny because you don't even know what sets him off like that. He's a monster."

All of the defensive linemen agree: The guy they all call "Big O" leads the team in that category — which probably comes as a surprise to outsiders who think that distinction belongs to the charismatic Cam Jordan.

Onyemata doesn't really have an explanation for it.

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"It's just in there," he explains. "That's just how it is. That's just who I am."

Onyemata has recorded 4½ sacks, 35 tackles and four tackles for loss this season.  

The Saints will count on him to be even more productive in Sunday's NFC championship game against the Los Angeles Rams. It'll be the Saints' first game without defensive tackle Sheldon Rankins, who suffered a torn Achilles tendon in last week's divisional round victory over the Philadelphia Eagles.

"He's not going to have to be Superman in this game," coach Sean Payton said. "He'll just have to continue playing like he's been playing."

Onyemata is in his third NFL season. This will be the biggest game of his 26-year-old life, a win away from playing in the Super Bowl.

Unlike most of his teammates, Onyemata didn't grow up dreaming to play on football's grandest stage. Heck, he didn't grow up dreaming about playing football. In fact, he never touched a football until 2011, a year after the Saints won their first Super Bowl. He was 18 at the time, having just moved from Nigeria to attend college at Manitoba in Canada when he first started playing football.

"He was 11,576 snaps behind everyone else," Payton said, referring to Onyemata having never played high school football. "To his credit, he's worked extremely hard to get to where he is now."

Seven years later, Onyemata has an appreciation of just how far he's come in such a short amount of time.

"It's been amazing," Onyemata said. "Growing every year and improving every year, and that's just kind of how I have taken it."

Football, he says, "is still foreign" to his parents back home in Nigeria.

But Onyemata has picked up on the game just fine. He has played a key role in the success of the defense this season. The Saints finished the regular season second in the NFL against the run, and they were fifth in the league in sacks.

"He had very limited football knowledge when he first got here," Saints defensive coordinator Dennis Allen said. "He's such a quick learner. It's one thing to learn assignments and what you're supposed to do in certain situations. It's another thing to instinctively be able to react when things happen on the field. That's where his progression has come."

Onyemata's ability to catch on so fast is one of the reasons his teammates love lining up beside him. Tyeler Davison, Stallworth and Onyemata will all be part of the rotation in the middle of the line, looking to fill the giant void left by Rankins.

"Whenever you have a guy like David, who's naturally gifted, big and strong and athletic and serious about doing his assignment with the right fundamentals and technique, that's damn near an unstoppable combination," Davison said. "So the sky is the limit for him."

And while Onyemata makes a big play, showing off that potential, he'll likely let you know about it.

Locker-room Onyemata won't. But gameday Onyemata will.

"Big O has a mean streak on game day," defensive end Alex Okafor said. "When you get that man going, you've got to fear for your life. But that's what you need. You need guys that play with that edge on Sundays. Big O keeps to himself and is quiet and chill — but on game day, somehow we get the monster up out of him."

Follow Rod Walker on Twitter, @rwalkeradvocate.