Advanced Stats

The #StevensEffect ☘️ – Advanced “coaching effectiveness” stats & Celtics injuries

Brad Stevens - Boston Celtics coach - photo credit: Boston Celtics

As the injuries mount, the Boston Celtics have one thing going for them: Brad Stevens. By reputation, Stevens both puts players in a position to succeed, and helps develop them as a season rolls on.

But can this anecdotal eye-test observation be verified by data? Is there, as some have said, a measurable #StevensEffect?

It’s a question that many have asked but few have tried to calculate. Following on celtics247’s preliminary hypothesis in part 2 of “The Stevens Theory,” I decided to have a crack.

For this analysis, I used the very method I previously employed in order to quantify the impact of the ever-underrated Bill Russell.

Brad Stevens - advanced stats - measuring coaching impact on player peformance - NBA coach of the yearEssentially I will look at player performance (approximated by Win Shares) with or without Brad.

The first thing that is remarkable is the churn: Brad has already coached more players in his 5 seasons (57) than Russell had teammates for his entire career (51). This gives us a good sample size to work with.

That said, I’ll cut to the chase. Stevens-coached players have produced 31.7 WS over what we would have expected based on their career rates and minutes played. The biggest improvers: Isaiah Thomas (+9.3), Jae Crowder (+8.9), Avery Bradley (+8.0), Zeller (+4.2). Biggest disappointments: Gerald Wallace (-3.0), Jared Sullinger (-1.5), injured Rajon Rondo (-1.2).

Kyrie Irving wins the per-minute improvement award, producing 0.228 WS/48 against 0.149 WS/48 for his career and leaving me with egg all over my face. (This after expressing reservations about Irving’s likely value to the Celtics Reddit page in, “Mythbusters: Kyrie Irving edition,” last October.)

But wait, there’s more. This isn’t the sixties anymore; we have much better metrics than WS.

According to Boxscore Plus-Minus, Brad’s players have overperformed by a staggering 51.4 wins.

The list of players is similar, except Sullinger goes from 2nd-worst to 4th-best, replaced in his former spot by Kelly O, who’s having an outstanding year for Miami.

This also assumes Brad is having no effect on the 14 players who have had no other coach. If he’s improving them to the same degree, that’s another 7.8 WS or 12.7 wins by BPM.

Stevens’s value

Let’s put a dollar figure on this. Taking an average of the WS/BPM figures (even though BPM is better) and conservatively assuming the effect is halved among the players for whom we have no comparative data gives us 10.8 additional wins per full season.

The market value of an NBA win in 2018 is approximately $2.5M in player pay ($101 million salary cap divided by 41-win average). So free agent Brad would command $26.6M annually, trailing only Gordon Hayward and Al Horford in salary.

The people who called Stevens our superstar weren’t kidding. No wonder Danny Ainge originally signed him for 6years and $22 million and extended it for an undisclosed amount a couple of years ago.

Seen in this light, there may even be a #StevensEffect feedback loop on the Celtic roster and salary cap. Hmmmm.

Notes and resources

1. All data per, accurate as of 10 March.

2. Discuss this article in the comments section below, on Reddit, or on the #StevensEffect thread on Twitter.

3. More from Teh_Noob on Celtics247:

Bill Russell, ’68 Finals: 3 triple doubles, triple double avg. – the mounting evidence,” February 16, 2018.

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u/teh_noob -- -- is a regular contributor to r/NBA, r/BostonCeltics, r/sports, and other pages on Reddit. Among his signature pieces are a series on "Mythbusting" Danny Ainge's performance in the NBA draft; research on Bill Russell's place in history and statistical achivements, and the defensive improvement of Kyrie Irving.

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