In the Bucs heyday, they used to pride themselves on tackling. They didn't have a flashy offense, they couldn't score points, but there's one thing they did well: the Tampa Bay Buccaneers could tackle.
You can throw that out the window now. By Football Outsiders' Broken Tackles metric, the Bucs were the fourth worst tackling team in the NFL. They had at least one broken tackle on 70 plays, or 7.1% of all defensive plays. This used to be so different. Derrick Brooks was perhaps the best tackler in the NFL, Ronde Barber the best tackling cornerback in the NFL and John Lynch the hardest hitter. But this is the cost of undersized players in the NFL, and the Bucs have long built their defense on speed over size.
This is in evidence with another team that still runs a Tampa 2 defense. The Indianapolis Colts try to limit spending and find diamonds by ignoring size. As a result their special teams suffer and their defense is always porous against the run. Their defenders tend to be a little more injury-prone than those of other teams. The upside is that the Colts never have problems plugging a hole if a linebacker goes down. They just bring in the next undersized but speedy linebacker they drafted in the sixth round, and there's little dropoff.
But another team that has also run a Tampa 2 defense for years does know how to stop the run: the Chicago Bears. They have been successful in no small part because Lance Briggs and Brian Urlacher are big for their positions. Urlacher is 6'4" 258 lb and Briggs is 6'1" 240 lb. Contrast those two with 6'2" 231 lb Barrett Ruud and 6'1" 226 lb Geno Hayes.
The Bucs have taken notice of what the Bears and other teams with bigger players (mostly 3-4 defenses) have done. They have added size to their defense over the past years, as most recent additions Tyrone McKenzie and Mason Foster are significantly bigger than the other linebackers on the roster. Aqib Talib and Myron Lewis are significantly bigger than the prototypical Tampa 2 corner. And Adrian Clayborn and Da'Quan Bowers are far cries from slim edge rushers like Dwight Freeney and Simeon Rice. The only position on defense where the Bucs don't seem to crave size is the safety position.
That's not to say that there's no room for undersized but fast players on the roster: Geno Hayes has been a solid player for the Bucs. But they're not convinced that drafting speed over size is the answer anymore, and seem to go with instinctive, big but slightly slower players instead. Expect the run defense as that philosophy makes its effects field. And maybe then the Bucs can go back to tackling again.