Why Steve Kerr's Season Is the Best by Any NBA Rookie Coach Ever

When the Golden State Warriors beat the Dallas Mavericks on April 4, Steve Kerr set a new NBA record for wins by a rookie head coach. 

The Warriors celebrated the accomplishment by giving Kerr the game ball and, much to Kerr’s surprise, a shower:

Sure, he inherited a 51-win team, so it’s not like he had to build them from the ground up. But is he having the best season ever by a first-year skipper?

Has he been even better than that?

The Rookie Head Coach Comparison

I first looked at everyone I could find whose team topped 50 wins in his inaugural season at the helm. In the chart below, the further to the right the circle is the better the winning percentage. The closer to the top, the more the team improved from the previous version. Hover over a circle to see the details:

As you can see, three circles stand out. Gregg Popovich’s is way up at the top. He improved the San Antonio Spurs' winning percentage 47.6 percent his first full season.

Kerr’s circle is furthest to the right, as he has by far the best winning percentage.

And the Chicago Bulls’ Tom Thibodeau’s is the one between them. He’s second in increase and tied for second in winning percentage.

Improvement and Success?

So how much credit do you give for improvement and how much for success? That’s not easy to state because, while percentage increase gives you a nice number to work with, improvement isn’t a constant. It’s much easier to go from 10 to 15 wins than from 60 to 65.

Statistically, there’s something called “standard deviations,” which are helpful in measuring something like that. The easiest way to explain them is to use something most people are already familiar with: IQs and geniuses.

Standard deviation is a measure for a population where about 68 percent of events will fall within one range and 95 percent within a second one. The average IQ is 100, and the standard deviation is 15. Ergo, 68 percent of the population has an IQ between 85 and 115 and 95 percent between 70 and 130.

Those marks—70 and 130—then become significant. An IQ below the former is one of the three criteria used when determining intellectual disability, and one over 130 is considered to be genius level. Only about 2 percent of the population falls into each category.

From there, 2 percent of each group will be another standard deviation away from the mean. So, someone with a 145 IQ will be one of the two smartest in 10,000 people, and someone with 160 will be just two in a million.

The point of all this is that the more standard deviations away from average an event is, the more rare it is.

To apply this principle to the topic at hand, I compiled the records of every team season in history—all 1,393 of them—and determined the standard deviation was 15.07 percent. I then divided them into “bins” consisting of half a standard deviation each. You can scroll over each bar to see exactly how many occurrences fall into each one:

Notice how the longest bars are near the center, and they get shorter on the ends. That confirms once you get past around the 56 percent win mark (around 46 wins) each additional improvement gets more difficult to achieve.

Popovich’s team, with a winning percentage of 68.3 percent, is in the third bin from the right. Thibodeau’s, at 75.6 percent, is in the second. And in that little bar at the end, consisting of just six teams, you have Kerr’s Warriors.

In fact, the Warriors are 2.18 standard deviations away from the mean. And anything over 2.0 is considered statistically significant. In essence, Kerr’s season is the “genius” equivalent of records. So the improvement from 51 to 68(ish) wins is actually the most impressive of the three.

Simple Rating System

Winning isn’t the only measure of success. In fact, the general convention these days is that margin of victory matters more than just wins and losses. A team that wins nine games out of 10 by 100 points is probably better than a team that wins 10 out of 10 by 10 points.

Additionally, just looking at records doesn’t consider strength of schedule.

At Basketball-Reference.com, there's something called “Simple Rating System” or SRS, which factors in both of those things. I also looked at standard deviations and SRS. Again, each bin indicates about half a standard deviation:

The Warriors have an SRS of 10.58, which is the sixth highest in history. They’re in that little itty-bitty bin, all the way to the right.

Seven teams in history have had an SRS over 10. Here they are:

Season	Tm	W	L	W/L%	MOV	SOS	SRS
1970-71	MIL	66	16	0.805	12.26	-0.34	11.91
1995-96	CHI	72	10	0.878	12.24	-0.44	11.8
1971-72	LAL	69	13	0.841	12.28	-0.63	11.65
1996-97	CHI	69	13	0.841	10.8	-0.11	10.7
1971-72	MIL	63	19	0.768	11.16	-0.46	10.7
2014-15	GSW	63	13	0.829	10.72	-0.15	10.58
1991-92	CHI	67	15	0.817	10.44	-0.37	10.07

Michael Jordan headed up the three Chicago Bulls squads. The two Milwaukee Bucks teams had Kareem Abdul-Jabbar. And the Los Angeles Lakers boasted both Wilt Chamberlain and Jerry West.

Andrew D. Bernstein/Getty Images

Each of those teams had arguably one of the five—or even three—greatest players in history. The Warriors’ best player is Stephen Curry, who might be this year’s MVP, but he’s not in the conversation with Chamberlain, Jordan and Abdul-Jabbar.

Furthermore, the coaches of those teams were all established. Larry Costello was in his third year with the Bucks when they had their first big year. Phil Jackson was in his third with the Bulls.

While Bill Sharman was in his first season with the Lakers, he had previous NBA and ABA experience, including the 1970-71 ABA championship with the Utah Stars.

Kerr, on the other hand, had never coached a game at any level at any point in his life. The fact that he's having so much success in his rookie year is phenomenal.

Improvement on Both Sides of the Ball

The most remarkable thing about the Warriors’ improvement is that it’s mostly the same team as it was last year. The only player who has logged 1,000 minutes and wasn’t on the roster previously is Shaun Livingston.

Popovich had some extreme circumstances on his side. David Robinson was out for most of the season prior, and that enabled the Spurs to win the lottery. They chose Tim Duncan with that pick. So much fo the Spurs dramatic "improvement" was the issue of effectively adding two Hall of Fame players. 

With Thibodeau, while the core of the team, Luol Deng, Joakim Noah and Derrick Rose, all returned, they also added Carlos Boozer and a revamped bench. While coaching was a big part of their success, it wasn't the only part. 

Yet the Warriors have improved on both ends of the court. Last year, their offensive rating was 107.5 (12th in the NBA) and their defensive rating 102.6 (fourth). This year, they lead the NBA in both categories at 111.6 and 100.7.When you have the same players performing markedly better on both offense and defense under a new coach, that’s probably what’s making the difference. It’s an Occam’s razor thing.

No team in history has been better on both sides of the ball than these Warriors, and only the 1996-97 Bulls come close. In fact, only eight other teams have had an offensive rating over 109 and a defensive rating below 102. Their two-way dominance is among the best in history.

Season	Tm	W	L	W/L%	ORtg	DRtg	NRtg
1995-96	CHI	72	10	0.878	115.2	101.8	13.4
2014-15	GSW	63	13	0.829	111.6	100.7	10.9
2007-08	BOS	66	16	0.805	110.2	98.9	11.3
1993-94	SEA	63	19	0.768	111.1	101.5	9.6
2006-07	SAS	58	24	0.707	109.2	99.9	9.3
2001-02	SAC	61	21	0.744	109.0	101.1	7.9
1979-80	BOS	61	21	0.744	109.4	101.9	7.5
2001-02	LAL	58	24	0.707	109.4	101.7	7.7
2008-09	ORL	59	23	0.72	109.2	101.9	7.3

Kerr entrusted Ron Adams, his assistant, to manage the defense and Alvin Gentry, the associate head coach, with the offense.

Chris Ballard wrote for Sports Illustrated about how Kerr turned the Warriors into a juggernaut and how his assistants helped:

"

Under Adams, the Warriors run a “shell” protection scheme predicated on length, anticipation and the ability to think and act decisively. They switch most every pick and roll, taking advantage of all their interchangeable parts, and Adams expects everyone to contribute. To him, there’s no such thing as an innately poor defender. In Chicago, he helped Kyle Korver become part of a top defensive scheme and now he wanted to do the same with Curry. “I don’t think you’re a bad defensive player,” he told Curry last summer, “but you don’t play enough possessions well.” (He also said, “Prove to me you’re better than your dad.”) Steph embraced the challenge. Though he now regularly covers opposing point guards, he’s improved from an average to above-average defender, posting one of the top ten defensive ratings in the league while leading the NBA in steals, which he accrues without gambling in passing lanes.

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 And the offense?

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The result is a system in which the only sin is standing still. “Ball movement and people movement,” is how Gentry describes it. The bigs use dribble hand-offs, the shooters curve and cut in a continual churn and everyone, eventually, gets to touch the ball. To Kerr, who had the advantage of watching the Warriors up close as a broadcaster, this was the best way to utilize a roster stocked with bigs who are better-suited to passing than diving to the rim (in particular, Kerr calls Bogut “a witch with the ball.”)

"

The result is a team that swims with activity on both sides of the ball, offering not only wins, but ridiculous entertainment value. The Warriors are not just the best team in the NBA; they’re the most fun to watch.

When you put this all together, you have to wonder if there’s ever been a more impressive season by a coach at any level. Kerr stepped in without having any coaching experience and immediately turned an above-average squad into one of the six best in NBA history with no change in critical personnel.

And he did it on both ends of the court.

He's easily doing the best job by any rookie coach in history. And if he caps it with a title, it may be the best single season by a coach of any tenure.