Nylon Calculus: Ben Simmons is one of the NBA’s most versatile defenders

In a bygone era, perhaps a 6-foot-10 kid would have grown up on a steady diet of Moses Malone or Kevin Garnett highlights the minute he laid eyes on a basketball, looking up to the patron saints of the interior that came before him. But not Ben Simmons.

“As soon as I was on the court, my dad told me to be creative and do what you want at a young age. I never thought about being a big guy and going to the post,” Simmons told Jessica Camerato of NBC Philadelphia.

That early encouragement has manifested itself into a player with little to no parallel in the modern NBA. Simmons is a true point guard with the size of a power forward or center. He’s not simply a point forward who sometimes brings the ball up the court and is a gifted passer. He runs the Philadelphia 76ers offense and is capable of making any read on a basketball court.

Simmons’ unique profile has enabled head coach Brett Brown to create an “inverted” offense around Philadelphia’s franchise cornerstones, that maybe more than anything, is emblematic of today’s positionless NBA. Simmons will roam around the post and seal his defender, while Joel Embiid, the 76ers’ nominal center will stretch his own man out to the 3-point line and neutralize the opposing bigs. Simmons, a passing savant, immediately spots the open channels in the defense. Three points, easy as you like.

And yet, Simmons’ offense is arguably the less impressive part of his overall game. He cultivates chaos on offense. He’s an ultimate chess piece on defense, equal parts perimeter hound and paint patroller. It’s rare for rookies to have a positive, winning impact. It’s even rarer for rookies to come off the blocks hot on the defensive end, with so much schematic and off-ball complexity. Simmons’ Defensive Real Plus-Minus of 1.75 ranks fourth in the league among all rookies, trailing only the Warriors’ Jordan Bell, the Lakers’ Lonzo Ball, and Utah’s Royce O’Neal. Bell, though, plays only 14 minutes a game, O’Neal has played less than a thousand minutes total on the entire season, and Ball’s team, while recently ascendant, is still headed for the lottery, whereas Philadelphia is the No. 6 seed in the Eastern Conference.

Ben Simmons’ combination of size, strength, and agility gives him an advantage on defense that few other players in the NBA enjoy. His identity on that end is predicated on his ability to pick up any player at any spot on the floor. The phrase “he can guard 1-5” is thrown around a little loosely to refer to versatile defenders, but in Simmons’ case, it couldn’t be more spot on.

Using the NBA’s recently released matchup box score data, we can chart out how many possessions each game Simmons spends guarding guards, wings, and big men. Employing that three-position taxonomy, the below ternary plots lend themselves to easily observing the distribution of defensive possessions that he uses up guarding each spot.

Juxtaposing Simmons’ game observations against both his fellow teammate and Defensive Player of the Year candidate Joel Embiid as well as his contemporary in a scintillating Rookie of the Year race, Donovan Mitchell, reveals clearly the remarkable nature of his defensive profile. There are just as many games where he has spent most of his time matched up on guards as there are ones where he’s been primarily responsible for wings or big men.

When we discuss versatile players, names like Draymond Green and Anthony Davis typically dominate the conversation. They’re some of the league’s most switchable defenders, with the demonstrated effectiveness to back up their “rover” tendencies. However, Ben Simmons is forcing himself into that discussion, with a marriage of quantity and quality that is so critical when it comes to talking about versatility.

To better approximate that effectiveness, I’d like to introduce my defensive versatility index, a metric that functions just as the name suggests. Chris Pickard and I created a version of this statistic in the NBA Analytics Hackathon back in 2016, but now that the NBA has made matchup data available, it became possible to design a slightly less granular public variant (though with some improvements as well).

In a nutshell, using the same three-position taxonomy as described earlier, I modeled for each player the differential between points per true shooting attempt (field goals plus shooting fouls¹) faced and the positional average on each individual matchup, normalized for the 3-pt shooting ability² of the offensive player and the overall level of the team defense. This results in three raw differentials, one against each position: guards, wings, and bigs.

I weighted each differential by the number of attempts faced against the respective positions, and then, perhaps most critically, applied a set of cascading adjustments (penalties/multipliers to each weighted differential) around a framework of rules to better illustrate true defensive versatility:

1. It’s not good to have a positive differential (since this indicates that the player performed worse than average against a given position).
2. It’s worse to have positive differentials against multiple positions.
3. Positive differentials are bad on their own, but their negative impact is exacerbated if it’s against a position where the player faced a significant fraction of their defensive shot attempts.
4. Negative differentials are good, but they don’t represent versatility if that impact is clustered primarily against one position.
5. Having negative differentials against all three positions while facing a significant number of attempts against all three positions is the versatility bingo.
6. If the player is overall a bad defender though (based on Defensive Box Plus-Minus), they should be penalized as such.

Rule No. 6 comes into play for the final step of the index calculation, a weighted average (70/30 split) on the adjusted defensive versatility impact and the player’s DBPM. The final results are below, a table of the best defensive versatility indices so far this season. The more negative the value, the more comprehensive the total on-ball defensive impact.

That’s quite a list. Al Horford is the Defensive Player of the Year candidate, but shout outs to Bloodsport and Randle Hill! LRMAM’s inclusion in this list also underscores just how important a free agent signing he was for the Western Conference-leading Houston Rockets. Everyone on that list ranks in the top 25 in RPM Wins amongst their respective positions, with the exception of Michael Kidd-Gilchrist (who ranks 26th among small forwards). It’s notable that eight of those top ten players weigh at least 225 pounds and are at least 6-foot-9. The strength afforded by those frames form a common thread amongst versatile defenders, not the least of whom is Simmons himself.

Ben Simmons’ athletic gifts are numerous, but his strength particularly stands out, to both opponents and teammates. To hear Justin Anderson, the 76ers’ 228 pound small forward tell it, “I told him afterwards, ‘There’s only one other guard who makes me feel small, and that’s LeBron.’”

Paired with his superior dexterity, Simmons is a force to be reckoned with down in the post, able to match up with his man step for step while not ceding an inch of space. Among all guards who face shot attempts within six feet of the basket on at least 20 percent of their defensive attempts (minimum 35 games played), Simmons is seventh in defensive field goal percentage at 57.2 percent, forcing opponents to shoot 4.8 percent below their average rates near the rim.

Just take a look at how he dogs Lauri Markkanen, the Bull’s own talented sweet-shooting rookie power forward, into a forced flip shot that harmlessly misses the rim.

Simmons is equally fearless though closing out on guards beyond the arc, even when that guard happens to be Kyrie Irving. In most cases, the Celtics would be ecstatic to force Al Horford’s man to switch onto Irving, as they get in the play below from Horford’s screen. However, Simmons calmly steps up and even manages to get a piece of Irving’s 3-point attempt.

That sort of block on a switch or rotation isn’t new for Simmons either. From parsing the matchup box-score data, almost half (46 percent) of Simmons’ blocks are as a helper, where he records a rejection on the player who wasn’t his primary matchup on the possession. He expertly utilizes his preternatural instincts and length to turn every possession into a battle from anywhere on the floor. Among all players in the NBA Stats database, only five this season have accumulated 50+ blocks and 100+ steals: Ben Simmons, Andre Drummond, LeBron James, Josh Richardson, and Simmons’ own teammate Robert Covington.

Next: Nylon Calculus -- Damian Lillard, JaVale McGee, and reader questions

Prior to the start of the season, Brett Brown laid out his vision for Simmons’ defense. “I think that because of his versatility, he’s going to be able to put out a lot of fires,” Brown told reporters in September. “I think because of his foot speed and length, if he gets cross-matched on a point guard, I’m OK with that.”

Thus far, Ben Simmons’ has done nothing to dampen his head coach’s excitement. For years, Philadelphia fans would fill Wells Fargo Center with chants of “trust the process.” But the time of piling up losses and wishing on ping pong balls is past. Now, Philadelphia is gunning for home court advantage in the playoffs. Billboards to woo LeBron James are being erected around the city. And the 76ers’ precocious, versatile rookie from Australia is one of the biggest reasons why.

*All stats are current as of March 16^th.

^[1] Including free throws as part of shooting attempts paints a more complete picture of a player’s efficiency. For example, when judging a typical center’s scoring, it wouldn’t make sense to exclude their free throw percentage. This creates a sort of great equalizer between positions that closes the per-shot efficiency gap between the positions. Perimeter players take harder shots, but big men are typically worse at converting free throws – tradeoffs!

^[2] A lot of work has been done demonstrating that a large component of an opponent’s 3pt percentage is noise, in that it is harder to control for as a defender. As such, following the lead of Jacob Goldstein and others, accounting for an opponent’s 3pt percentage is a crucial adjustment, so as not to penalize or reward a defender too extremely for something they have typically less control over.