A startling defensive turnaround has led the metamorphosis in Fayetteville during the past month, a month in which Arkansas blanked a top-20 opponent and a top-10 opponent, became bowl eligible and asserted itself as the team no one in college football wishes to play.

The key to this in-season 180 is the hire of Robb Smith as defensive coordinator from the Tampa Bay Buccaneers.

Smith — a coordinator under Greg Schiano at Tampa and Rutgers prior to that — inherited a mess of a defense that often surrendered big plays and didn’t play as a complete unit in 2013 as the Hogs went 3-9.

The first-year coordinator arrived at Arkansas with his quarter-quarter-half scheme with an emphasis on tackling and fundamentals that derived his old boss’s scheme.

After Auburn scored 45 points in the season opener, the Hogs began to show improvement. Arkansas allowed just 28 points and 353 total yards to Texas Tech, and held Alabama to 2.1 yards per carry and 14 points in mid-October.

Smith’s defense ranks in the top 25 nationally in total defense, scoring defense and red zone defense. The Pennsylvania native told Fox Sports’ Bruce Feldman his guys turned a corner in the Nov.1 17-10 loss to then-No. 1 Mississippi State.

“We got back from the Mississippi State game and there was a sense,” Smith told Fox Sports. “We tackled the best we had tackled and we communicated really well. We really only had one communication problem and that had led to a touchdown.”

Since that game, Arkansas has yet to allow a single point. The Razorbacks pitched back-to-back shutouts against conference opponents for the first time since entering the SEC in 1992.

Perhaps even more impressively, the Hogs have allowed just one touchdown in its last 12 quarters — three games against ranked opponents.

Part of the style of football head coach Bret Bielema brought to Arkansas is stopping the run, exactly what Smith has focused on this season. He also had another goal; he wanted to eliminate the big plays that plagued the Razorbacks in 2013.

That required three components: improved communication, better tackling and keeping the football in front of you.

Smith felt the first two mandates clicked in the loss to the Bulldogs, but the third and final piece was still absent. Until last weekend when Arkansas forced six Ole Miss turnovers in a 30-0 loss.

The strength of the unit is the front seven, led by three impact players in Trey Flowers, Darius Philon and Martrell Spaight.

Flowers has recorded 12.5 tackles-for-loss and four sacks, while Philon, his inside counterpart, has added three recovered fumbles. Spaight anchors a much-improve linebacking corps. The senior has been a breakout star in Smith’s scheme, notching a team-best 108 tackles, eight tackles-for-loss, two forced fumbles and one interception. That’s after starting just two games last season under former coordinator Chris Ash.

Smith and Bielema worked together at Iowa early in their careers. When Bielema hired him in February — his fourth time attempting to hire Smith — he came alone from Tampa.

Smith didn’t even come with a graduate assistant. Thus, he had to teach his scheme to every coach and player.

The Razorbacks defense has played a pivotal role in the morphing we’ve seen from the Hogs this season. Smith’s defense is leading a confident Arkansas team looking to derail Missouri’s SEC East title hopes.

The Broyles Award — given to the nation’s top assistant coach — named Smith a semifinalist this week, a well-deserved honor. If Arkansas can close its season with three wins over ranked opponents and plus-four in win improvement, it will be because Smith’s defense leads the Razorbacks there.

Bielema has a burgeoning contender on his hands in northwest Arkansas, and it’s because he made the most underrated hire of the year.