The Chicago Bulls find themselves in sole possession of second place in the surprisingly crowded Eastern Conference. The team is currently riding a five game winning streak that has seen the team play some of its best basketball to date. The good vibes surrounding the Bulls can be attributed to the stellar play of Jimmy Butler, but his heroic performances aren’t the only reason the Bulls suddenly look like a real threat to dethrone LeBron and the Cavaliers.

The Bulls were 11-8 on December 9th, but their winning percentage was not telling the real story of the team. Chicago to that point had a net rating of +0.1, the mark of a .500 team and nothing else. Since that date, the Bulls have won 10 of their 14 games and are doing so with an encouraging net rating of +4.2, sixth highest in the league during that stretch.

The reason for choosing December 9th as the arbitrary cutoff point for the tale of two Bulls seasons is because on that date Nikola Mirotic was replaced in the starting lineup by Taj Gibson. The decision to start Taj, and break up the Niko-Gasol duo, has had one major impact on an under-appreciated aspect of the game: rebounding.

Prior to Taj being inserted into the starting lineup, the Bulls were 16th in rebound percentage, grabbing 49.8% of available boards. Since that date, the Bulls have hauled in 52.3% of their rebound chances, the fifth-highest rate in the league.

The surge up the standings is due almost entirely to a huge increase in offensive rebounding. Before December 9th, the Bulls offensive rebound rate was just 22%, 20th in the NBA. Since then, the Bulls have been grabbing 28.2% of offensive rebound chances, the fourth-highest rate in the league.

The boost in rebounding is not necessarily dependent on the presence of the athletic Taj Gibson. Instead, it seems that the Mirotic’s role reduction is the primary cause for rebound success. The Bulls rebound a team worst 47.9% of rebounds with Mirotic on the floor, and just 20.7% of offensive rebound chances.

Mirotic has been the Bulls biggest disappointment through the first third of the season. I’m already regretting the money I spent on his shirsey and the energy I spent attempting to get my girlfriend hyped for NIKOMANIA. It’s no surprise that Mirotic hurts the Bulls offensive rebounding when he spends most possessions hanging around the three point line. Nikola’s four percent offensive rebound rate is less than half of the current starting power forward. On the defensive glass, Mirotic has the third-highest rate on the team and is ahead of Gibson. But the team as a whole craters on the glass with him playing, suggesting that Mirotic is good at grabbing easy boards and doesn’t contribute much to overall team success there.

It has been a tremendous struggle to find a front court partner for Mirotic who allows the Bulls to survive on the glass. Paired with Gasol, the Bulls grab just 46.1% of rebounds, which would be dead last in the NBA. When he shares the court with Taj, the Bulls rebound an unfathomable 44.8% of opportunities.

Fred Hoiberg’s decision to re-insert Mirotic into the starting lineup at small forward has not covered up Niko’s deficiencies. The Tall Ball experiment is not a successful one. Going into last night’s game, in the 113 minutes that Pau, Taj and Niko have played together, the team’s net rating is -6.5 and their rebound rate is 44.5%.

The one point of optimism for the Bulls moving forward has been the energetic play of Bobby Portis. With the rookie on the court, the Bulls collect 54.0% of available rebounds, the third-highest on court rate on the team. More importantly, Portis’s rebound ability seems to be immune to the Mirotic effect. The sample size is a microscopic 47 minutes (before Tuesday night), but the team’s 53% rebound rate is very encouraging.