Not too long ago, NBA Math held a straw poll among its writers, prompting everyone to vote on midseason awards. Most of my choices were pretty boilerplate: James Harden as the MVP, Ben Simmons as Rookie of the Year, Victor Oladipo for Most Improved Player and so on. But when I got to Defensive Player of the Year, only one name came to mind, and it wasn’t the same one chosen by the majority, which collectively nominated Draymond Green.

It was Al Horford.

This selection is no way an indictment of Green’s defense. He is performing at his usual All-Star form, ranking fourth in defensive rating and sixth in NBA Math’s defensive points saved, while the Golden State Warriors boast the league’s second-best defense. No one should have qualms about the ballots cast for him, but voting for Warriors year after year does get a little tiresome—especially considering the Boston Celtics’ drastic paradigm shift. Horford has transformed the Celtics, playing the part of linchpin for one of the unlikeliest defensive turnarounds in league history.

With the departures of plus-minus darling Jae Crowder and perimeter-defender extraordinaire Avery Bradley, many doubted the Celtics could even maintain, much less improve upon, their tepid numbers from last season. They finished with the 12th-ranked defense (105.5 rating) and ended up as the 22nd-best rebounding team, numbers barely befitting a 53-win No. 1 seed. For 2017-18, though, they claim first place in points allowed per 100 possessions and seventh in defensive rebounding percentage—marks that have helmed  an early-season surge and 25-7 record.

 And Al Horford has led the charge.

Even with a statistical revolution that has altered the way we follow basketball, offensive stats are much easier to understand and digest than reciprocal defensive numbers ever will be. And that makes the value of a player like Horford hard to quantify.

He is 10th in net rating among players who play more than 30 minutes per game, with a staggering plus-9.7. He is eighth in defensive rating and seventh in defensive points saved, according to NBA Math’s TPA database. Horford has also upped his rebounding percentage, going from 18.3 from in 2016-17 to 21.7 this season, and his per-36-minute rebounding numbers have jumped from a career-low 6.1 defensive boards in 2016-17 to 7.7, a mark he hasn’t hit since 2012-13 in Atlanta. The Celtics also score an absolutely mind-boggling 16.3 points more than their opponents per 100 possessions with Horford on the court, which ranks in the 95th percentile, according to Cleaning the Glass.  

He is a high tide raising all boats; when he plays well, the team as a whole is better, even if his individual stat lines look mediocre. Take, for example, the 60-win season his Atlanta Hawks posted in 2014-15, when he averaged 15.2 points, 7.2 rebounds and 3.2 assists. He didn’t lead the team in a single major statistical category, and yet the advanced numbers paint him as the one of the most important players. He finished with a team-high 8.7 win shares and was responsible for 9.18 wins over replacement. He was also 16th in defensive points saved, with 113.38. Though the Hawks’ offense incited a lot of praise for its ball movement and shot selection, Horford anchored the league’s seventh best defense en route to a No. 1 seed and an Eastern Conference Finals appearance.

The situation is identical in Boston this season. Kyrie Irving is the player who coaches scheme to stop, while Horford, aka Silent Hero, serves as the defensive fulcrum. And instead of having the sixth-place defense, the Celtics grade out as the best in the league. He could be in better shape or surrounded by personnel who better accentuate his strengths, but something has clicked like never before for the veteran center.

His overall impact, like his team’s win total, is high.

Horford is a great team defender, but his individual versatility really sets him apart from other big men. This season, Celtics head coach Brad Stevens has given him some of the most difficult assignments, against which he’s yielded some staggering results.

In two games against the Philadelphia 76ers, Stevens called Horford’s number to defend redshirt rookie phenom point something Ben Simmons. He can be a trying matchup because of his 6’10” height—an advantage he frequently exploits when defended by opposing guards.

But Horford’s own length, as well as his ability to stay in front of Simmons, perplexed the first-year player, holding him to 11 points in the first matchup and 15 in the second contest. Simmons is shooting an atrocious 29.4 percent when Horford is on the floor versus 62.5 percent when he is off. Watch here how he picks up the point thingamajig at the top of the key and slides his feet to stay in front of Simmons, getting his right hand up to alter the shot:

Guards are supposed to feast on opposing bigs along the perimeter. But this time, he can’t shake the defense with the crossover dribble, and the Celtics come away with the rebound.

And Simmons isn’t the only Sixer who has felt the gravity of Horford’s defense; his running mate Joel Embiid has also suffered shooting woes. During the one meeting between Boston and Philadelphia in which Embiid played, he only managed 11 points, including a 3-of-8 performance when guarded by the opposing big. Watch here as Horford challenges the three-pointer then cuts off the penetration and forces the young center to rely on a fall-away shot:

Horford’s shifty feet and ability to keep Embiid out of the lane seemed to befuddle the 23-year-old, who usually loses rival bigs with his quickness. A combination of veteran guile, patience and lateral quickness renders Horford an elite on-ball defender, even in his 11th year. He is a particularly adept isolation defender, as he shows in the clip above, allowing a scant 0.83 points per play and a 40.5 effective field-goal percentage. And the Celtics trust him to pester almost any lengthy player who gives them trouble in half-court sets, including one of the league’s most uniquely gifted breakout stars.

In a November contest between Boston and the New York Knicks, it was Kristaps Porzingis who drew the short straw. Horford held the NBA’s eighth-leading scorer to 12 points on a horribly inefficient 3-of-14 magazine, including an 0-of-8 clip from three. But this time, it was Horford’s lower-body strength, not just his quickness, that helped him harass the 7’3” Latvian star. Here again, he stays in front of Porzingis, warding off dribble penetration and forcing the worst shot in basketball—the long two:

These defensive adjustments are interesting because they don’t just occur on switches; that’s the scheme in action. 

Horford guards the opposing team’s best player by design, despite the Celtics having two high-quality wing defenders in Jaylen Brown and Marcus Smart. This might be the secret to Boston’s transformation: by using the center to chase around wing players, Stevens can line up Aron Baynes against enemy bigs to limit offensive rebounds and have both Smart and Brown combat secondary and tertiary scoring options. And Horford’s versatility makes it all possible.

In short stretches, he has shown some good defense against Giannis Antetokounmpo:

LeBron James:

Carmelo Anthony:

And even Kevin Durant:

The laundry list of players Horford has thwarted includes MVPs, All-Stars and some of the NBA’s best burgeoning talents. And he’s getting it done in a myriad of ways. In those clips alone, you can see help defense, closeouts, post-ups and even perimeter stops—something centers aren’t typically asked to handle.

The Celtics also have an elite transition defense, ranking second in points per play and fourth in effective field-goal percentage, in large part because of Horford. The man in the middle is hustling back to alter and sometimes outright block shots:

The numbers show Horford is an elite defender, and the tape seems to agree.

While his block totals are nothing spectacular (29 this season, tying him with defensive stalwarts Alex Len and Victor Oladipo), teams shoot 2.5 percent worse when Horford is on the floor, including a 4.2 percent dip around the basket, which puts him in the 83rd percentile among rim-protectors, according to Cleaning the Glass. Both differentials, career bests by wide margins, lead you to believe this old dog has learned some new tricks while leading this young, feisty, revamped Boston roster.

The Celtics have experienced a culture change from last year’s free-wheeling, Isaiah Thomas-led offensive whirling dervish. They’re now a team that grinds out close games, and Horford has been at the epicenter of that about-face. Winning on the back of a staunch defense forges a much surer path to playoff success, and the Celtics ultimately have their eyes fixed on an Eastern Conference Finals rematch with Cleveland Cavaliers. Stevens is well aware of the lock-down talent Horford brings to the table, and in their second year working side-by-side, they seem to have found the perfect blend of on-ball and rotation looks to make life hell on the rest of the league.

Is all of this enough to warrant a Defensive Player of the Year vote?

With a shift of this magnitude, Horford has definitely put himself in the conversation.

Follow Alex on Twitter @AlexWestNBA.

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Unless otherwise indicated, all stats are from NBA Math, Basketball Reference or NBA.com and are accurate heading into games on Dec. 18.