Who should Ben Simmons guard in the playoffs?

The Philadelphia 76ers are not your typical NBA team. First of all, they’re much better than most teams. Their 49-27 record is fifth-best in the league. They’re also unusual in that their best five-man lineup has appeared in just 10 games, sharing the floor for only 161 minutes. For context, know that there are 56 five-man units in the league that have been on the floor together more often, per NBA.com.

Among the group of 61 units that have shared the floor for at least 150 minutes, however, the lineup featuring Ben Simmons, J.J. Redick, Jimmy Butler, Tobias Harris, and Joel Embiid ranks fourth in offensive rating, 12th in defensive rating, and third in net rating. And that lineup itself, like its usage and its performance, is more than a bit unusual. Butler and Harris only arrived in Philadelphia this season. Redick is far further along in his career than the others, and somehow appears to have the most energy of them all. Embiid sat out two full seasons, played just 786 minutes in his third year in the league, and has since become one of the handful of best players in basketball.

And then there’s Simmons. He is perhaps the most unusual player in the league. At 6-foot-10 he is the tallest point guard the league has ever had, and while in that sense he is maybe the prototype modern NBA player, he lacks the one skill 29 other NBA teams absolutely require from their lead ball-handlers: shooting. Simmons has attempted just 65 shots outside the paint all season, and only 26 of them have originated more than 15 feet away from the rim. Simmons’ combination of size, speed, power, and vision allows him to overcome this glaring hole in his game, to the point that he is still one of the league’s most effective, efficient, and effervescent offensive players.

Incredibly, though, Simmons may be even more unusual as a defender than he is as an offensive player. According to an analysis of Second Spectrum player tracking data conducted by Krishna Narsu, Simmons is one of only eight players in the league who has spent at least 11 percent of his defensive possessions guarding an opposing player at each of the game’s five positions. He’s one of only two to do so while also acting as his team’s primary ball-handler on the other end. The other is James Harden, though, and he arrives at those percentages largely because of the Rockets’ switch-heavy defensive system which was devised to mask his biggest weakness (defending in space) and accentuate his greatest defensive strength (guarding in the post).

Simmons, by contrast, arrives at his percentages because he is perhaps the most flexible defender a coach could dream up. That’s not to say he is the best defender, of course; it’s just that there are very few players who have Simmons’ size and length and can also spend long stretches of NBA games defending the opposing team’s point guard or the opposing team’s center, and have neither be the result of a switch, but a decision made by the coach to pursue that specific matchup.

And the matchups Brett Brown has decided to pursue with Simmons have changed quite a bit since the 76ers traded for Harris at the deadline.

Prior to the deal for Harris, Simmons spent approximately 55 percent of his defensive possessions guarding 3s or 4s, per Second Spectrum’s data, compared to only 25 percent of his time on either point guards or centers. The percentages have shifted in a meaningful way since the deal, though, as Simmons has spent 48 percent of his time on forwards and 34 percent of his time in either primary ball-handlers or pivot players.

Those shifting percentages have come with a trade-off for the team’s defense. Philadelphia has been at its best throughout the season when declining cross-matches and just having Simmons guard the opposing team’s point guard. That was true before the Harris deal and it’s been true since — and the defense has actually been a point better per 100 possessions with Simmons defending the lead ball-handler since the trade.

By contrast, using Simmons against the opposing team’s center has been a disaster defensively for pretty much the entire season. Like, worst defense in NBA history type of disaster. (The same is true when he defends 2-guards, and that doesn’t surprise, either. A 6-foot-10 guy having to chase shooters through waves of screens doesn’t seem like the best use of his particular set of skills.) And it’s there where we arrive at an issue for the 76ers’ defense. A big part of the reason the team is using Simmons on centers at all becomes clear when you look at the list of pivot men he has defended for at least 10 possessions in a given game since the Sixers acquired Harris.

See if you notice anything they have in common: Lauri Markkanen, Al Horford, Anthony Davis, Myles Turner, Luke Kornet, Brook Lopez, Nikola Jokic. Every single one of those players fit into the archetype of a space big, the kind of players with whom Joel Embiid is most likely to struggle, as we saw last year against the Celtics in the playoffs or earlier this month when Nikola Vucevic tore up the Sixers’ pick-and-roll defense.

Sliding Simmons onto one of those players while Embiid guards, say, Marcus Morris, Aron Baynes, Julius Randle, Thad Young, Domantas Sabonis, Noah Vonleh, DeAndre Jordan, or Paul Millsap makes a decent amount of rhetorical sense. But the Sixers are just not getting any stops in this configuration, either. The sample size isn’t enormous (around 650 possessions for the full season) but the numbers are bad enough to point a big arrow toward this not being a salve for the one major issue the team seems to have defensively. Certainly, it was worth experimenting with, but the Sixers might just be better off playing things straight up and countering opposing teams with their size — it might be the biggest advantage they have.