The Offbeat: The Utah Jazz' NBA-Best Home Court Advantage

Russ Isabella-US PRESSWIRE

The stats confirm: Energy Solutions Arena is home to the best home court advantage in the NBA. How does this happen, what causes it, and how much of an impact does it have on Utah's performance?

APBRmetrics, the group of fans who study basketball statistically with the Association of Professional Basketball Research, have an awesome forum that displays some of the foremost advances in statistical basketball analysis at work. Today, in particular, I wanted to look at one ABPRmetrics user's (Eternal) research, and what it means for the Jazz. If you'd like to follow along with the thread at the APBRmetrics forum, it is here.

Home court advantage has long been a topic of discussion for basketball analysts, mainly because it makes no sense whatsoever. The game is played on the same 94 feet by 50 feet, the rims and balls and backboards are all league mandated to be exactly the same, and the players practice their shots literally tens of thousands of times so that their form is more-or-less identical every time, no matter if the shot is at home or on the road.

In a talk, at the 2011 Sloan Sports Analytics Conference, economist Tobias J. Moskowitz took a look at why home court advantage actually happens.

In the video above, Moskowitz explains the largest reason behind home court advantage: unintentional referee bias. In short, if you isolate all of the things referees don't have an effect on whatsoever, they're exactly equal for the home and road team. For example, whether or not a player makes a free throw is not at all influenced by a referee, but might be influenced by the screaming crowd with thundersticks. However, there's just no difference: the home team and the away team make the same percentage of their free throws. The subjective referee calls, though, like traveling, charge/block calls, etc. are called significantly more for the home team, especially if that team has a large crowd: traveling, for example, is called 25% more for the home team in soldout NBA games than their sparsely attended equivalents.

With that in mind, let's take a look at Eternal's data from the APBRmetrics forum. The following is a ranking of the teams with home court advantage with regards to the league average home court advantage from 2002 to 2013.

team | home
-----+-------
UTA | 1.019
DEN | 1.014
IND | 1.009
SAC | 1.009
GSW | 1.008
LAL | 1.008
CLE | 1.008
POR | 1.005
SAS | 1.004
ATL | 1.002
ORL | 1.002
PHO | 1.002
WAS | 1.002
CHA | 1.001
MIL | 1.001
DAL | 1.001
NOK | 1.000
MEM | 1.000
MIA | 0.999
BRK | 0.999
SEA | 0.998
CHI | 0.998
LAC | 0.996
TOR | 0.996
HOU | 0.996
NJN | 0.995
OKC | 0.995
DET | 0.993
CHH | 0.993
NOH | 0.992
MIN | 0.990
BOS | 0.990
NYK | 0.988
PHI | 0.988

Utah leads the pack, with Denver coming in second. What this suggests is that altitude has an effect as well, something Moskowitz didn't look at. It may not be the main factor, however, as Utah has a significantly higher home court advantage than Denver does, even though Denver has a higher altitude. I suspect Utah's rabid fans, plus the more vertical nature of our seats (many of our opponents have commented that it seems as if "the fans are on top of the action") mean a more intimidating environment for referees. Let's go ahead and look at the offensive and defensive impacts of home court:

team | hca_offense | hca_defense
-----+-------------+-------------
ATL | 1.007 | 1.005
BOS | 0.990 | 0.999
BRK | 1.000 | 1.001
CHA | 0.999 | 0.997
CHH | 1.001 | 1.008
CHI | 0.991 | 0.993
CLE | 1.001 | 0.992
DAL | 1.006 | 1.005
DEN | 1.011 | 0.997
DET | 0.994 | 1.001
GSW | 1.014 | 1.006
HOU | 0.988 | 0.992
IND | 1.003 | 0.994
LAC | 0.991 | 0.995
LAL | 1.006 | 0.998
MEM | 1.003 | 1.003
MIA | 0.998 | 0.999
MIL | 1.005 | 1.004
MIN | 0.994 | 1.004
NJN | 0.996 | 1.001
NOH | 0.993 | 1.001
NOK | 0.998 | 0.998
NYK | 0.996 | 1.008
OKC | 0.997 | 1.002
ORL | 1.000 | 0.998
PHI | 0.988 | 1.000
PHO | 1.005 | 1.004
POR | 1.008 | 1.004
SAC | 1.011 | 1.002
SAS | 1.002 | 0.998
SEA | 0.996 | 0.998
TOR | 0.999 | 1.003
UTA | 1.005 | 0.987
WAS | 1.004 | 1.002

Again, 1 here is league average home court advantage. Interestingly, Utah's offense is only helped somewhat more than league average (offensively, Utah's home court advantage ranks only 8th in the league), but defensively, Utah's home court advantage is league-best. Given the results above, this larger difference indicates that either:

  1. Altitude effects teams more offensively than defensively. That is, the lack of oxygen and tiredness means less efficient offense more than worse defense.
  2. Referee bias hits harder on defense, that is to say, rather than calling more fouls in favor of the home team on offense, referees simply don't call fouls on the home team on the defensive end.
  3. Some combination of the above, or something I haven't yet considered.
So how do these numbers impact the Jazz? Let's look at an example of how they work. League average home court advantage is roughly 1.0167 on offense, and 0.9835 on defense, for a total league average home court advantage of 1.035. In addition, the Jazz have a 1.005 times better home court advantage than league average, and a 0.987 times better defensive advantage. The Jazz this season are scoring 107.1 points per 100 possessions on offense, and allowing 107.0 points on defense. Thus, if we do the calculations, we get:

Expected points scored per 100 possessions = 107.1 * 1.005 * 1.0167 = 109.43 ORtg

Expected points allowed per 100 possessions = 107.0 * 0.987 * 0.9835 = 103.86 DRtg

In short, just due to the influence of home court advantage, the Jazz at home are 5.5-6 points per 100 possessions better than normal! Now, this calculation is at least a little misleading because the Jazz actual offensive and defensive ratings already account for how well the Jazz play at home, but you start to understand the impact that the Jazz home court has on their overall performance. On the other hand, a team like Philadelphia, at the bottom of the home court advantage ratings, would only have about a 1.5 point home court advantage per 100 possessions. That's a sizable advantage: even if you divide it by half (because you only play half of your games at home), it's still enough to move a team up about 5 slots in ORtg-DRtg differential. Basically, ESA's home court advantage adds at least a couple of wins per season onto Utah's total.

This is an incredible finding, and it starts to speak to just how good Jazz fans are. The energy from fans, funneled into impacting referee decisions (as explained by Moskowitz), along with altitude and some good stadium construction, make Energy Solutions Arena the hardest place to play for opponents in the NBA.
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