Should Nikola Mirotic Start for the Chicago Bulls Instead of Joakim Noah?

The Chicago Bulls look to have a bit of a position battle on their hands this season.

Pau Gasol -- fresh off both a EuroBasket MVP award, and a renaissance NBA season in which he averaged 18.5 points, 11.8 rebounds, 2.7 assists, and 1.9 blocks per game -- has his starting spot in the Bulls' frontcourt all but locked up. The real question emerging out of Chicago this offseason is: who will be his running mate?

It was Joakim Noah's job last year. In fact, Noah has started in all but 2 of the 323 games he's played for the Bulls over his last five seasons, earning a Defensive Player of the Year Award for his 2013-14 campaign and racking up three All-Defensive, one All-NBA, and two All-Star appearances in the process.

His displays of infinite heart and hustle on both ends of the basketball court are well known, but last season's averages of 7.2 points, 9.6 rebounds, 1.1 blocks, and 44.5% shooting from the floor all represent five-year lows for the big guy. His dipping numbers and repeated appearances on the injury report for numerous ailments are becoming unmistakable signs of a decline, and it's a growing concern in Chicago.

With new Bulls coach Fred Hoiberg in town, it's hard to say where his alliances will be when it comes to his rotations. Couple Noah's downward trajectory with the tantalizing upside of last year's Rookie of the Year runner-up, Nikola Mirotic, and this is starting to look like an open battle for starter's minutes going into training camp. Both Noah and Mirotic have implied as much this offseason.

If that happens to be the case, who is the better choice?

Noah has all the intangibles that you want in a star and team leader: he works hard, he puts it all on the line on both ends, he plays hurt, and he makes for a fun interview. There might be a bias among Bulls supporters for these reasons, but who do the numbers suggest would be a better option for Chicago going forward?

Offense

To his credit, Joakim Noah is a superior passing big man. He led all NBA centers in assists per game (4.7), Assist Percentage (22.7%), and Assist to Turnover Ratio (2.54) in 2014-15. That is one area on offense where Noah is clearly a better option than Nikola Mirotic (1.2 assists per game, 10.2% Assist Percentage, and a 1.09 Assist to Turnover Ratio).

And that's about where his advantages on offense end.

Yes, Noah shoots a better percentage from the field overall (44.5% to Mirotic's 40.5%), but when you factor in Niko's free throw percentage (80.3% to Noah's 60.3%) and his three-point prowess (99 made at 31.6% compared to Noah's 2 misses), Mirotic is clearly the more efficient shooter and scorer. To wit, his True Shooting Percentage (which measures twos, threes, and free throws) of 55.6% was the third best on the Bulls last season, and a fair bit better than Noah's 48.2% (10th on the team).

We know that Mirotic is more valuable than Noah as a shooter and stretch big, but he was also more efficient last season when it came to the more traditional offensive responsibilities of a big man, according to Synergy's Play Type Statistics):

Mirotic's points per possession (PPP) marks were substantially higher than Noah's both in the pick-and-roll and in the post, and while Mirotic didn't grade out as an elite roll man, he was worlds better than Noah on the post.

Defense

As a former Defensive Player of the Year, one would expect that the nod would go to Noah on this end of the floor. The problem with just giving him the benefit of the doubt in that regard, however, is that 2014-15 Joakim Noah did not perform at the level of 2013-14 Joakim Noah on defense.

For that matter, 2014-15 Nikola Mirotic wasn't that far removed from 2014-15 Noah in terms of defensive efficiency when measured by Defensive Rating, Defensive Win Shares, and Defensive Real Plus-Minus:

Of course, we haven't really pinpointed the best one-number metric to classify real defensive impact just yet (although DRPM is becoming increasingly respected), but rim protection is almost universally considered an important component of a big man's defensive value.

In 2013-14, Noah was a beast in that regard, allowing a stingy 47.2% on the 7.7 shots he faced per game within five feet of the hoop. Mirotic's 2014-15 rim protection numbers aren't exactly pretty (55.2% allowed on 3.5 shots faced), but Noah's 2014-15 (51.7% allowed on 6.2 shots faced) bares almost no resemblance to his Defensive Player of the Year campaign the year prior and wasn't really that much better than Mirotic's rookie season.

Throw in the fact that their careers are trending in opposite directions, and the gap between the two might grow even smaller as the 2015-16 season progresses.

Overall/Conclusion

With the league progressing more and more heavily to small-ball and the use of stretch fours, it wouldn't be surprising to see rookie head coach Fred Hoiberg go away from Tom Thibodeau's trusted two-big lineups (of the seven most-used lineups by the Bulls last season, five of them included both Noah and Gasol). The most logical candidate to join the starting five in order to effectively stretch the floor -- over other frontcourt candidates like Taj Gibson, Doug McDermott, and Bobby Portis -- would be Nikola Mirotic.

In that instance, Gasol could shift from power forward to center (where he's played 66% of his career, according to Basketball-Reference.com), and Noah could come off the bench. From a pure numbers standpoint, Mirotic already looks like a more efficient option for the Bulls over Noah anyway:

The resulting starting five of Derrick Rose, Jimmy Butler, Mike Dunleavy, Mirotic, and Gasol played a fair number of minutes together last year (with Noah missing 15 games), and actually fared quite well. In fact, they were even more efficient defensively as a unit than the equivalent lineup with Noah in place of Mirotic, without giving up much in terms of rebounding:

Of course, a calculator won't make this decision for the Bulls; it will be up to Fred Hoiberg. If he sticks with the local hero for his starting five by choosing Noah, that would be understandable, as Noah will likely come back this season with a lot to prove.

In the meantime, if Hoiberg goes in another direction and inserts Nikola Mirotic in Noah's place, it seems like the numbers would back up his decision.