How do you make an NFL captain?

Well, you can start by signing an undrafted free agent from the University of Wisconsin, a guy who most people think is too short and too small to play linebacker in the NFL. You give him mostly special teams jobs and in the biggest game of the year — the biggest game of your life, really — you call for an onside kick to start the second half of Super Bowl XLIV and tell the rookie to go get it.

“[He] made a really good special teams player when he first got into the league because he could run,” Saints coach Sean Payton said.

He hurts his foot in the final preseason game of his second NFL season, but you stick with him. You develop him. You continue to use him sparingly on defense but on a lot of special teams units. He manages to collect three sacks in his third season, recovers two fumbles in his fourth.

“[He] was a young guy running around in 2012,” recalled Steve Spagnuolo, the defensive coordinator with the Saints for that one season. “He was a backup and great special teams player. I remember at the end of that season saying that we should have played him more in sub packages.”

After four seasons in New Orleans you let him go in free agency. He’s not a star player. He’s important, yet completely replaceable.

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“Sometimes a player like that gets out of our building and you look back and think, ‘Man he could run, what would we have done different?’ ” Payton said. “But he’s someone that there wasn’t any specific reason [he left] other than in the end, we weren’t able to keep them all.”

You sign him in Tampa Bay, where he starts just four games at linebacker but finishes second on the team in special teams tackles. Midway through his second season with the Bucs, you trade him. Trade him to the most successful franchise in the past 15 seasons. The Patriots.

ANOTHER RING

“He was a hell of an athlete,” said Shane Vereen, a running back on that New England team. “He’s a guy who can run. He was the first linebacker who could consistently run with me. We built a relationship off that.”

You have him win another Super Bowl ring and have another dominating special-teams performance in the big game, this time one that you win in the final seconds on an interception. Now he’s a guy with two championships to his name, an impressive resume. But he’s never been a starter.

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You bring him to the Giants. You bring him home with a three-year, $10.5-million contract to play just a short drive away from where he grew up in Jersey City and where he first stepped on a football field at New Brunswick High School. He’s part of a group of signings designed to bolster the special teams and, if he can, the defense.

“[It’s] fortunate that he was out there for us,” coach Ben McAdoo said. “He’s come in and done a nice job. He has grown into one heck of a linebacker and one heck of a special-teams player.”

A STEP BACK

In his first year with the team it doesn’t really work out as well as hoped. For anyone, really. He starts seven games at linebacker — a career high necessitated by an insurmountable number of injuries and inexperience at the position — on a 6-10 team that finishes last in the NFL in total defense. He’s playing through his own injuries, but appears in 15 games, also a career-high. He never seems quite comfortable on the field. He could be a bust.

But you stick with him. You overhaul the defense in the offseason, even change the head coach, and decide he’s one of the players you’ll keep.

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“Sometimes people have to bounce around before they find their niche, find their spot,” Giants linebacker Mark Herzlich said. “I know he’s definitely done that. Given an opportunity here, he’s taken advantage of it. He’s earned the opportunity to be where he’s at.”

You stand back and watch as the player, now in his eighth season in the NFL, now healthy, begins to flourish. In a league where players are constantly cannonballing in and rookies like Odell Beckham Jr. and Carson Wentz make immediate impacts, he’s a late bloomer. But he blossoms nonetheless.

He has a dominant summer, flying around the fields of training camp and preseason games, and establishes himself as one of the team’s clear leaders both vocally and football-wise.

“Early on you can always tell that there are a few guys who stick out before you even get to the on-field stuff,” said cornerback Leon Hall, who signed with the Giants during this summer’s training camp. “He’s been one of those guys, for sure, who stick out from the crowd. I never set out looking to find out who is the leader of the team. They kind of just show their face naturally and you recognize it as a fellow player.”

“Personally I don’t think he’s been anywhere long enough to gain the body of work to be in that position, but he’s always been one to stand up and speak what’s right and do the right things,” said Vereen, now a running back for the Giants. “Having a year in the system and coming back with the same system has got to be a relief. He’s been bouncing around.”

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CAPTAIN, OH CAPTAIN

Then you let the players select the leader of their own defense. And they chose him, even though he’s never been a full-time starter in the NFL, to follow in the footsteps of Harry Carson and Michael Strahan and Justin Tuck and Antonio Pierce.

“I voted for him,” Hall said proudly. “On any team just because you have guys who make Pro Bowls or are statistically among the top in the league consistently doesn’t necessarily make them captain material. We don’t vote on statistics. We just vote on ability to lead us.”

“I was really excited for him,” Herzlich said, “and I thought it was well deserved.”

Finally, you send Jonathan Casillas out for the coin toss on Opening Day in Dallas with a C on his chest, where he shakes hands with President George W. Bush at midfield then comes back and leads the team with 10 tackles to help give the Giants a 1-0 record for the first time since 2010.

You wonder why it took so long. You wonder where it still can reach.

“I guess it can happen a lot of different ways,” Spagnuolo said. “He’s been to a couple different teams, won a Super Bowl in two different spots, so he knows what it looks like. He’s been sharing that a little bit with these guys who haven’t been around it. How you do it, what it’s supposed to look like. He talked with the defense at the end of last Friday’s practice. He spoke really well about that. He’s been encouraging since he’s been here.”

“It doesn’t surprise me at all,” said Payton, the first to pick him out of the crowd, with a mix of regret and pride. “There’s a growth that takes place with players. I think it’s extremely important to him, the game. I think when you have someone that’s passionate like that and talented, those are traits that you look for in a captain.”

And that’s how you do it.