There is one way and only one way to play the game and Mathias Kiwanuka believes — with strong endorsements from his teammates and coaches — he embodies that singular approach. “From the time I walked out on a football field it’s been ingrained in me that when you step on the field somebody knows that you’re there’’ Kiwanuka said. “Because they got hit.’’ That temperament makes Kiwanuka a respected member of a defense that until proven otherwise is the weak link a Giant-sized question mark. Antrel Rolle says Kiwanuka is “definitely a closet tough guy’’ because of his reserved outward demeanor. “He’s such a nice guy and very mild mannered very soft spoken’’ Rolle said “but when you need some disruption out there on the field you call nine-four.’’ Ask defensive line coach Robert Nunn about Kiwanuka and one word is immediately used. “We need some toughness in there’’ Nunn said of the defensive line room where Kiwanuka now resides full time as he’s no longer a linebacker. “And he’s a tough person naturally.’’ The question facing the Giants is this: Are there enough natural tough guys on the defense? It didn’t look that way last season as the unit tumbled to 31st in the NFL and showed an alarming weakness against the run — always the litmus test for toughness. Kiwanuka isn’t sure. He identified to The Post who he feels are true “tough guys’’ on the Giants defense and his list was interesting for who made the cut and who did not. “As a group you’re going to have your highs and lows that’s just how it is but there has to be individuals you can always point to’’ Kiwanuka said. “Hands down Chris Canty was going to be out there fighting no matter what. When you had a Barry Cofield you knew he was going to be out there. You had Antonio Pierce you know he was going to be out there fighting. “Ok so now those guys are gone. Who’s going to be the guys to step up? You can point to a Linval Joseph and say ‘OK this kid is tough whether the game is out of hand or whether it’s on the line.’ You have Antrel Rolle in the back and you have Jacquian [Williams] out there and you know he’s going to hit if somebody pushes him in the back he’s going to turn around and take care of the situation. Not saying he’s going to do anything dirty. I think at every level defensive back linebacker and D-line you need to have more than one guy who’s going to be out there and a tough guy no matter what.’’