Analysis of the NBA Coach of the Year Award: a comparison between the official voting and objective techniques

Authors: Julio del Corral (@jdelcorraltm) and Andrés Maroto (@jazzandmar)

Steve Kerr won the NBA Coach of the Year Award last 26^th of April. 130 media members from USA and Canada, that regularly cover the North American basketball tournament, were involved in the voting. The coach of Golden State Warriors did not receive the award last year when he led the Californian franchise to win the tournament and achieved the highest number of victories that season. However, he received the award this year after Golden State Warriors set the NBA regular-season record of victories of all times (73-9), surpassing the 72-victory Chicago Bulls from the 1995-96 season. In fact, Kerr played for Phil Jackson back then. Kerr, who is the third Warriors’ coach achieving this award (after Alex Hannum and Don Nelson), will have to share the prize with his assistant coach Luke Walton. The team was led for the first 43 games (39-4) by Walton, as Kerr was recovering from back surgery.

Kerr received a total of 381 points (64 first-place votes), which is only 46 points ahead of the runner-up, Terry Stotts, head coach of Portland Trail Blazers. Stotts qualified the Portland’s franchise for the play-offs against all odds in the 5^th West ranking position. Portland is actually fighting a spot in the West final against the Kerr’s Warriors these days. Gregg Popovich (3^rd) from San Antonio Spurs, Steve Clifford (4^th) from Charlotte Hornets; and Dwane Casey (5^th) from Toronto Raptors completed the list.

Previous research shows that this sort of award usually goes to the coaches from the strongest teams not only in the NBA but also in other sports (e.g., soccer). Nonetheless, coaches that are able to obtain a better performance by optimizing their resources and squads should be awarded. During recent years, we have published similar posts analyzing the efficiency of NBA coaches since 1993. For that purpose, we evaluate objectively the performance of each coach comparing their results with those expected from betting odds. The probability of winning each game is implicit in these odds and allows us to calculate the probability function of the number of victories in a season for each team and coach.

The following table shows the results for this season:

Team	Coach	Efficiency	Victories	Eff. Ranking	NBA Ranking
Golden State Warriors	Steve Kerr	0.99	73	1	1
Toronto Raptors	Dwane Casey	0.96	56	2	4
San Antonio Spurs	Gregg Popovich	0.93	67	3	2
Charlotte Hornets	Steve Clifford	0.93	48	4	10
Portland Trail Blazers	Terry Stotts	0.89	44	5	12
Miami Heat	Eric Spoelstra	0.81	48	6	7
Los Angeles Clippers	Doc Rivers	0.81	53	7	6
Denver Nuggets	Michael Malone	0.78	33	8	22
Dallas Mavericks	Rick Carlisle	0.78	42	9	14
Memphis Grizzlies	Dave Joerger	0.72	42	10	15
Detroit Pistons	Stan Van Gundy	0.69	44	11	13
Washington Wizards	Randy Wittman	0.65	41	12	17
Boston Celtics	Brad Stevens	0.56	48	13	9
Orlando Magic	Scott Skiles	0.52	35	14	20
Indiana Pacers	Frank Vogel	0.48	45	15	11
Chicago Bulls	Fred Hoiberg	0.47	42	16	16
Milwaukee Bucks	Jason Kidd	0.47	33	17	23
New York Knicks	Derek Fisher / Kurt Rambis	0.44	32	18	24
Cleveland Cavaliers	David Blatt / Tyronn Lue	0.43	57	19	3
Sacramento Kings	George Karl	0.37	33	20	21
Minnesota Timberwolves	Sam Mitchell	0.35	29	21	26
Atlanta Hawks	Mike Budenholzer	0.34	48	22	8
New Orleans Pelicans	Alvin Gentry	0.29	30	23	25
Utah Jazz	Quin Snyder	0.27	40	24	19
Brooklyn Nets	Lionel Hollins / Tony Brown	0.27	21	25	28
Los Angeles Lakers	Byron Scott	0.23	17	26	29
Oklahoma City Thunder	Billy Donovan	0.20	55	27	5
Houston Rockets	Kevin McHale / JB Bickerstaff	0.18	41	28	18
Phoenix Suns	Jeff Hornacek / Earl Watson	0.04	23	29	27
Philadelphia 76ers	Brett Brown	0.03	10	30	30

Our results show that the first position is the same either with the official ranking or using our methodology. Other coaches also hold a pretty accurate efficiency-ranking of victories relationship (not only coaches from the higher ranked teams, e.g., Casey, Popovich, Spoelstra or Rivers, but also coaches from the lower ranked teams, e.g., Hoiberg, Karl, Gentry, Scott or Hornacek). This method also identifies the worst coach of the year, Brett Brown from Philadelphia 76ers. In general, the correlation coefficient between both measures is 64%.

There is little discussion among fans and media experts about the best coaches this season as Kerr, Stotts and Popovich showed an outstanding performance (apart from highlighting the performance of Walton leading the Warriors in the first games of the season). In fact, all of them might still improve their numbers as they are coaching their teams in the conference semifinals at the moment.

Nonetheless, we can observe significant differences in other teams. Steve Clifford (Charlotte Hornets) would be the 4^th best coach of the year with a higher efficiency than Terry Stotts. Other coaches underrated according to the final number of victories are Michael Malone (Denver Nuggets) or Rick Carlisle (Dallas Mavericks). On contrary, coaches whose teams are still competing in the conference semifinals, i.e., Tyronn Lue, who substituted David Blatt in the second half season, would go down to the 19^th position of the ranking, even though Cleveland Cavaliers finished in the 3^rd position according to the ranking of victories. In a similar way, Billy Donovan, Oklahoma City Thunder coach (5^th position), would go down to the 27^th position in terms of efficiency, or even Mike Budenholzer, Atlanta Hawks coach, who won the NBA Southeast Division last year.

Finally, another interesting point is that the change of the coach has not resulted in great improvements in general as all teams that did it (Knicks, Nets, Lakers, Cavs, Rockets or Suns) are below the efficiency average (i.e., 53%).

We think these awards should not only be based on the total number of victories at the end of the season. Our methodology has limitations but it is a good starting point for the development of an objective ranking, which seems to be in line with NBA fans opinions. Because of all this, the voting system could be substituted for some kind of scientific objective indicator (see the one proposed here) to award the official prizes at the end of the season.

Special thanks to Carlos Gómez González

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