Marcus Smart is literally the worst shooter in the NBA, at least right now. Of any player averaging at least 10 shots a game, Smart has the worst field goal percentage, league-wide, at 28.1 percent. Of all players with at least 1,800 shots in their career, Smart has the 57th lowest mark in NBA history.

It's not just jumpers, either. Smart is shooting 36.7 percent on layups this season, 10th-worst in the league. In non-post-up situations, Smart is in the 2nd percentile league-wise in shots around the rim via Synergy Sports. (That means 98 percent of the league is better.) Smart has shot 9-for-35 on unguarded catch-and-shoot jumpers, which is only slightly better than his 7-for-30 mark on jumpers off the dribble.

OK, so Marcus Smart is a terrible, horrible, no-good shooter who clearly must be a liability to the Celtics.

Except ... when Smart is on the floor, the Celtics outscore their opponent by 11.3 points per 100 possessions (roughly a game). That's 7.9 points per 100 possessions better than when he's off the court. In other words, the Celtics jump from a solid team to an elite team when Smart is on the court.

But that's obviously the defense, right? After all, Smart is an omni-defender who can match up with all five positions, a bull in a china shop. The Celtics' defense is 1.5 points per 100 possessions better with him on the floor. That's where the good play comes from, right?

Except ... here's the thing ... when Smart is on the floor, the Celtics have a 106 offensive rating. That's also second-best among rotation players, and 6.8 points better than when he's on the bench.