TAMPA – Should it eventually come down in this way, we now know what it is that will keep undrafted rookie linebacker Riley Bullough from earning a roster spot with the Tampa Bay Buccaneers this season.

It won’t be a lack of competitiveness, leadership traits or work ethic. The long-haired Michigan State product who has emerged as one of the real stars of the HBO series Hard Knocks has all of that.

What he’s lacking is mobility. That was made clear during Tuesday’s episode of Training Camp With The Tampa Bay Buccaneers, when the camera’s peaked inside a player evaluation session.

As Bucs general manager Jason Licht and the team’s coaches sat around a large boardroom table analyzing the qualities of the players fighting for roster spots, linebackers coach Mark Duffner delivers the dirt on the kid who has been dubbed “Joe Dirt’’ by his teammates.

“This kid’s a highly competitive leader, a guy who works at everything, knows the defense,’’ Duffner said. “He’s everything you’re looking for – toughness, awareness, study, confidence, it’s just that he’s limited movement-wise.

“I like the kid’s competitiveness. I think he’s a guy that, like I said, movement’s going to be his issue. I don’t know that we’re going to be able to overcome that with him. But I’m pulling for him.’’

It’s hard not to. The kid is a gamer. And we learned in this episode that while Bullough comes from a family of very handsome means, “he doesn’t play like a trust-fund kid,’’ Licht said.

Bullough’s family, by the way, is a football family, one that has produced at least three NFL players and a coach. Still, Bullough has his work cut out for him if he’s going to make this team.

The numbers at the linebacker position aren’t in his favor and we saw during the Bucs loss to the Browns last Saturday night just how it is that that lack of mobility is working against him.

After two impressive outings, Bullough failed to bat away a short pass he was in position to break up and then failed to keep pace with another pass catcher during the Browns game-winning touchdown drive.

It’s hard to tell if the context is accurate, but defensive coordinator Mike Smith responded by echoing what Duffner said earlier, saying, “You can see why Riley’s not going to … You know, (he) can’t make a play.’’