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The 20 most important assistant coaching hires of the 2020 season -- No. 20: Zach Arnett, Mississippi State

Back by overwhelming demand, FootballScoop will once again examine the assistant coaching hires that will have the biggest impact on the college football season and the coaching job market in the 2020 season and beyond.

Who: Zach Arnett, Mississippi State

Title: Defensive coordinator/linebackers coach

Previous stop: San Diego State defensive coordinator/linebackers coach (2018-19), linebackers coach (2014-17), graduate assistant (2011-13).

Why he’s important: After close to 15 years at the feet of Rocky Long, Zach Arnett has taken his first job apart from the wing of his mentor -- and what a job it is, matching wits with the likes of Gus Malzahn and Chad Morris at Auburn, Jimbo Fisher at Texas A&M, Steve Ensminger and Scott Linehan at LSU, Steve Sarkisian at Alabama, Kendal Briles at Arkansas and Lane Kiffin at Ole Miss.

Before we move forward, let's spend some time on how Arnett got to Starkville.

He played linebacker for Long at New Mexico from 2005-08, and as a senior he was a team captain and led the nation in forced fumbles. After two years away from the game, Arnett began his coaching career under Long at San Diego State, then steadily climbed the ladder, from GA, to linebackers coach, to defensive coordinator. It would be hard to imagine Arnett having a thought about defensive football that Long didn't think first.

Arnett continued Long's 3-3-5 scheme through last season, placing two ends, a tackle, a Mike, Will and Sam in front of three safeties -- a field Warrior, a boundary Warrior, and an Aztec. (Expect those terms to be left behind in San Diego.)

“We hope it’s unique and difficult to prepare for,” Arnett said earlier this year. “I do think you’re seeing more multiplicity, variation in schemes that teams are running, you are seeing more 3-3-5 looks, a lot more of it on third down than on first or second, but with the purification of the spread and teams going sideline to sideline, there’s been an effort by defenses to get more athletes on the field and guys that can run and cover space.”

The Aztecs did not sacrifice strength at the point of attack in the name of speed, either. Only Georgia allowed fewer rushing yards than San Diego State in 2019, permitting just 75.4 yards per game on 2.75 a carry. In fact, Arnett's Aztecs were the only team in FBS to hold opponents below 1,000 total rushing yards (980).

In news that was both good and bad, San Diego State was just so-so in producing negative plays, ranking just above 50th in tackles for loss and sacks. While that shows the Aztecs were not especially disruptive, it also means their run numbers weren't built by a bunch of 10-yard sacks that obscured a high number of explosive runs allowed. They just straight up stoned people.

SDSU also ranked sixth in the country in pass efficiency defense, swiping 18 interceptions against just 10 touchdowns allowed, which added up to a unit that rated seventh in yards per play (4.65) and second in scoring (12.7).

Arnett inherits a unit that rated 107th in yards per play and 73rd in scoring. The 2019 Bulldogs needed a miracle to reach a bowl game, and Arnett will likely need to improve upon those numbers to keep Mississippi State's program-record streak of 10 consecutive bowl trips alive.

The switch from Joe Moorhead's RPO-based offense to Mike Leach's Air Raid could involve some growing pains. For instance, Bulldog quarterbacks combined for nearly 200 rushes last season; Washington State ran the ball 210 times -- total. (Leach has secured two transfers, including ex-Stanford QB KJ Costello, who's likely to start Day 1.)

Leach's first Washington State team actually saw its scoring average drop by 9.4 points per game, so the success of Mississippi State's 2020 season could hinge on how quickly Arnett adapts from the Mountain West to what has quickly become the most challenging offensive divisions in college football.

For instance, take a look at State's October schedule: vs. Texas A&M, at Alabama, at LSU, vs. Auburn.

Arnett's new scheme needs to click and do so quickly, or 2020 could be a long season in Starkville.