In a typical year, the NBA’s All-Star break offers the league’s most dysfunctional contenders a chance to reset, take inventory and right what ails them heading into the final stretch before the playoffs. This season, thanks to Cleveland’s moves at the trade deadline, the post-All-Star watch likely will fall to the Oklahoma City Thunder and how it weathers the loss of Andre Roberson, the beating heart of its defense.After an offseason that included acquiring Paul George and Carmelo Anthony to combine with reigning MVP Russell Westbrook, the Thunder expected to compete at the highest levels. It hasn’t worked out that way. The team is 33-26 at the break and has lost six of its last nine games. There are all manner of reasons for this, from the obvious difficulties of integrating three high-usage stars to the decline of key players on an already-thin squad. (Offseason acquisition Patrick Patterson, who was a reliable stretch 4 for years in Toronto, has disappointed and tanked the offense while he’s been on the court.) Despite all that, the team seemed to have figured something out by January, when it ran off eight straight wins on the strength of its defense and a newly thriving offense. But late in that stretch, Roberson went down with a ruptured patellar tendon. He was lost for the season, and the Thunder had a whole new sort of crisis.Roberson is a singular player in the NBA. He is one of the best perimeter defenders in the league, and at 6-foot-7, he has the size and quickness to guard four positions. Roberson’s effect on the Thunder defense is tremendous. He can switch practically any matchup, cover opposing stars and not only challenge their shots but also dissuade them from even attempting them. His defensive Real Plus-Minus — a stat that heavily favors big men — ranks fourth in the league. Overall, the defense was 12.5 points worse per 100 possessions when he left the floor. His effect doesn’t grade out at quite the same level of Golden State’s Draymond Green or Utah’s Rudy Gobert, but he just about maximizes the impact a perimeter defender can have on a game.Or as Westbrook put it: “I think people outside our building, people across the world always complained about different things Andre didn’t do instead of embracing all the great things he did do. I’ve always embraced Andre and I was always very, very happy he was on my team because of things he did on both sides of the ball. Setting screens, cutting, running the floor. A lot of things that you can’t teach.”Those “things Andre didn’t do,” of course, refer to Roberson being one of the worst regular offensive players in the league. Roberson is a notoriously inept and unwilling shooter. He is shooting 22 percent from the 3-point line this season on a diet of wide-open shots the opposing defense is thrilled to see him take. And yet, his overall effect on the offense doesn’t seem to have been as dire as advertised.Since Roberson went out, Oklahoma City’s defensive rating has been 112.3, which would rank 27th in the league, ahead of only the Cleveland Cavaliers, Sacramento Kings and Phoenix Suns. That’s extreme though not unexpected with Roberson no longer there to cover for weaker defenders like Westbrook or Anthony. But here’s the kick in the head: The team’s offensive ratings has barely budged despite losing one of the worst offensive players in the league, going from 110.9 before Roberson’s injury to 111.8 after it. This is much harder to explain.Roberson didn’t simply deprive his offense of a player who could do a better job of shooting, passing or dribbling. He shrank the court, allowing defenders to roam guilt-free, to harass ballhandlers and make life difficult for anyone establishing post position or running around off-ball screens.So clearly the team would be expected to show more improvement than it has in his absence. But while the overall offense has been flat, the individual stars have thrived with Roberson out. With Roberson on the floor, the Thunder pick and roll barely worked at all, producing just 87 points per 100 chances, according to data from Second Spectrum. It didn’t much matter if it was Westbrook handling the ball (90 points per 100 chances), George (73), Raymond Felton (91) or Carmelo Anthony (94). Without Roberson there, the team’s pick-and-roll points jump to 95. Westbrook and George see especially large jumps without Roberson, landing at 100 and 91 points per 100 chances created on the pick and roll, respectively.It gets stranger: George produced only 77 points per 100 chances on drives with Roberson on the floor; without him, that shot up to 96 — on a significant number of shots. Westbrook, too, goes from 98 points per 100 chances to 105, or the difference between Ish Smith and Victor Oladipo this season. And while Roberson didn’t actually affect the team’s effective field goal percentage overall, both Westbrook and George suffered large drop-offs in their shooting numbers when they shared the court with him.But the Thunder have yet to capitalize on the additional space available with Roberson out. Westbrook has played well in some ways, creating at James Harden/Chris Paul levels on the pick and roll, and poorly in others, shooting just 43 percent from the field and 18 percent from the three in the games since Roberson’s injury. George has been hot from the three — he’s hit at least five 3-pointers in four consecutive games — and has averaged 29.6 points on a 62 effective field goal percentage through those 10 games. But Anthony has gone absolutely dormant, and both he and Westbrook missed two games to injury.There’s plenty to be encouraged by over these past few games. George looks like a different player without Roberson, and all may be right if he and Westbrook are both firing at close to optimal levels by the playoffs. Further, second-year shooter Alex Abrines, seeing increased minutes with Roberson out, has run hot and cold, shooting 35 percent on threes overall since the injury. That should improve over time.But even so, the offense taking a dip despite subtracting a guy who may be the single worst offensive player who’s actually allowed to play s troubling, and Oklahoma City doesn’t have an obvious source of those unteachable qualities Westbrook mentioned — the cutting, the running, the screens. The Thunder’s stars may finally have the room to operate as stars, but its problems are now ones not solved easily by star power.Check out our latest NBA predictions.