The Boston Celtics’ 2015-2016 season expectations has been a point of contention between qualitative and quantitative fans. Many subjective fans are estimating that they will hover around .500 and battle for the 8 seed in the East. On the other hand, quant models are projecting the Celtics to flirt with the 2 seed in the East. Let’s explore both sides of the argument.

Why the Celtics Might Be Stuck In Neutral:

The Celtics won 40 games last year, but they so handily overachieved that perhaps their success was in part due to luck. Amir Johnson is a nice role player, and Marcus Smart should be better, but the team still lacks the star to take them to the next level. Amir does not have the athleticism that he did in his prime, and Smart does not have the burst or handle to become a stud scorer. While the roster is generally young, it lacks standout athletes and it is fair to expect whatever slight progressions made to simply overcome the regression to the mean. After all, it is commonly doubted that the Celtics have a single above average starter.

Vegas’s Westgate tends to agree with this narrative, as they set the Celtics’ regular season win total o/u at 42.5.

Why the Celtics Might Be Poised For a Leap

First, let’s look at the key returning pieces and their bb-ref ages from last season:

The average minute weighted age of this group is 23.8. Suffice it to say that all key returning pieces are more likely to improve than they are to regress. This also applies to their 38 year old coach, as Stevens is likely still improving as he enters his 3rd NBA season.

The piece with most growth potential is Smart. He does not appear on track to become an offensive star, and I do not anticipate that he will suddenly be able to run an efficient NBA offense at age 21. But he did have an outlier good defensive season for a rookie (as predicted by yours truly), and a healthy leap forward on defense complemented by mild to medium offensive improvements is plausible. RPM rated him as the top rookie last season, and a moderate sophomore leap will make him a solidly good player.

Key departed players:

Rondo and Green were widely presumed to be the Celtics’ best players among casual fans entering last season, until Boston became better after dealing them and their respective new teams got worse. Their level of harmfulness to the Celtics can be disputed, but at worst the Celtics shed almost 1800 slightly bad minutes that will be comfortably upgraded this season.

That leaves Brandon Bass as the only noteworthy loss. Bass is a perfectly decent rotation player, but he is slightly undersized as a PF and is neither a rim protector nor floor spacer. There is no argument subjective or quantitative that he will be missed, as consensus is that his replacement Amir Johnson will be a clear upgrade.

Johnson has long been a darling of advanced stats. His bad ankles have caused his athleticism to wane, but at age 28 he still has enough left to contend for most valuable player on the Celtics. Here are his early blurbs from training camp (as per Rotoworld)

9/27:

Celtics head coach Brad Stevens said that Amir Johnson looked “terrific” during his first practice with Boston.

9/28:

Amir Johnson has shined on defense in practice so far.

9/30:

Celtics head coach Brad Stevens praised Amir Johnson for his defense again on Tuesday:

“First of all, he’s 6-9, he’s long, he’s athletic,” Stevens said. “But then I think there’s not a lot of people like that generally, but there’s a lot of people like that in this league. But his mind is excellent for defense and he really prioritizes it. And then his motor is extremely high. So I think that all that factored in is why he’s separated himself as helping your team win when he’s on the defensive end of the floor.”

Stevens’s instant adoration for Amir is a solid checkmark in favor of the verity of advanced stats painting him in a favorable light. He is in decline due to his ankles, but he gets a boost by transitioning from an average coach to an elite one and should seamlessly fit into any Celtics lineup.

The Celtics also get a full season of availability from two of their more important players in Jae Crowder and especially Isaiah Thomas. Crowder has impressed at least one basketball expert:

Mavs also gave up a really good player in Crowder. Great defender and has developed into a decent offensive player.

Haralabos is one of the few NBA fans who works to precisely discern the value of players, and he has become a millionaire by succeeding at this. Like Smart and Johnson, Crowder is piece underrated by the masses as his value stems from defense and intelligence to avoid mistakes offensively. Having him for a full season where he possibly starts and displaces lost Jeff Green minutes will certainly be healthy for Boston.

Isaiah Thomas can nearly be treated as a new acquisition, as he only played in 21 games for the Celtics and averaged 26 minutes per game coming off the bench. He gave the roster of one way perimeter defense studs a sorely needed ball handler, and led the team in a myriad of advanced stats as he played a huge role on offense and did so efficiently. Here’s the split from Isaiah Thomas’s first appearance in a Celtics uniform. Note that PD = point differential:

Sample W L PD Pre-Zeke 20 32 -1.6 Zeke 20 10 3.2

The +3.2 PD during the Thomas era puts them right at a 50 win expectancy over a full season. And he only played 37.5% of possible minutes over this stretch as he missed 9 games.

The +3.2 was likely unsustainable over 82 games, as Thomas is not LeBron James and the prior 52 games cannot be entirely neglected. But given that Thomas and Crowder are better than Rondo and Green (small sample support: units with IT and Jae were +7.4 per 48 in 440 mins, Rondo and JG were -2.2 in 568 mins together), it intuitively makes sense to give less weight toward the earlier sample. It follows that the end year Celtics were likely better than their 40 win bottom line (41.4 wins derived from PD).

This is all one sided arguing in favor of the Celtics being better, so let’s discuss why they might be worse. It is not clear that any of their young guards among James Young, Terry Rozier, or RJ Hunter will be above replacement level, so the Celtics may be unable to stomach serious backcourt injury issues without trading for a guard.

The other risk is that new acquisition David Lee is a clear downgrade from the other 5 bigs on the roster. If he carves out a significant rotation role, this could harm the Celtics’ team output. But other than that, the Celtics are clearly trending in the positive direction.

Conclusion

People are not hardwired to intuitively assess the precise impact of each player and coach, let alone the summation of these over a full 82 game season riddled with variance. Most fans tend to overrate scoring, underrate defense, and have a skewed perception of what constitutes a valuable player. Thus it is easy to describe the Celtics as a team with “no above average starters” and resonate with casual fans, but there is no substantial evidence to support this claim. Even if the claim is humored and the Celtics only have 5 average starters and a good bench, why is it difficult to believe that Brad Stevens can elevate such a roster to 48-50 wins in the East?

Stat models like the Celtics because the team is loaded with subtle edges in their favor. Every key data point suggests improvement, and there is little to no clear force pushing the Celtics in the negative direction. While basketball stats have their limitations, they have the advantage of objectivity and freedom from cognitive biases.

On the other hand, the subjective arguments against the Celtics are entirely founded on cognitive biases since they center around lack of perceived star power. It would be compelling to make a case that last year’s playoff appearance was heavily fueled by luck, that the Celtics’ advanced stat stars have holes in their game that stats fail to capture, or that the pieces on the roster will fail to mesh. But a central argument that the roster looks underwhelming to your unscientific eye is the level of approach that caused the masses to initially believe the Celtics lost the Rajon Rondo trade with Dallas.

I am on #teamstats. In this instance, they present a reasonable approximation of the truth, and people who enjoy money can freely bet Boston o42.5 wins.