Reduced homecourt advantage?

[mtamada]

Noticing that there are a number of teams this season who have road won-loss records that are as good or even better than their home records, I wondered what teams' home won-loss records have looked like this year. Through Saturday, teams were 322-285 at home, 53.0%. A remarkable number for the NBA. In 2013-14, the home won-loss percentage was 58.0% and in 2012-13 it was 61.2%.

This season is only half over; maybe just by chance the weak teams have been playing most of their games at home but that doesn't seem to be the case. The teams that have records of .400 or lower have collectively played only 3 more games at home than on the road.

Is this a random blip, or is something different this season?

[Crow]

It would help to know the home win%s of the playoff level teams and the lottery teams for this season and past to see if the rate of change is different for the groups. Also how much has the net point differentials changed? A small movement in reducing net point differential could have a bigger impact on win% but that is speculation on one possibility.

Has there been a noticeable change in the home / away net foul differential?

What do the fg% look like? Detective work to be done.

[Mike G]

This year's home/away differences:

Code: Select all

14-15   FG%   3fg%   2fg%   eFG%    FT%   3fgr   FTr   As/FG
home   .454   .353   .491   .501   .755   .267   .282   .593
away   .449   .348   .485   .495   .751   .266   .274   .577
                        
per G   ORb    TRb    Ast    Stl    TO    Blk    PF     Pts
home   10.9   43.2   22.4   7.71   13.7   5.0   20.4   101.2
away   10.6   42.5   21.5   7.64   14.0   4.6   20.9    99.4

Home MOV is 1.80 ppg. This should produce a W% of about .562, not the .530 we've seen. Apparently, visiting teams have been winning an inordinate share of close games, or home team stats are padded by more blowouts, or both.

Indeed, visiting teams are 39-22 in games decided by 1 or 2 points.
If that advantage were just 31-30, home teams win .543 of games.
Road advantage is just 87-84 in games decided by 5 or less.

There have been 58 games that the home team has won by 20 or more. Just 29 such blowouts by visitors.
If we reduced all 20+ MOV games to exactly 20, the adjusted avg is +1.4 ppg for the home team.
Apparently the disparity between home/away W% and MOV is due to both : disproportionate close wins on the road, and blowouts at home.

[Crow]

Home team with 0.5 personal fouls. Small, but a notable part of home court advantage this year. Wonder what the average is for prior years.

Home win% for east .419, for west .653. Probably a lot of west close road wins and west blowout home wins due to conference imbalance.

[BigLeagueInsights]

Good question Crow, here's what I get:

Away 2000 22.48866499
Home 2000 22.14069082
Away 2001 21.40454163
Home 2001 21.01429773
Away 2002 21.96383516
Home 2002 21.50126156
Away 2003 21.77291842
Home 2003 21.10344828
Away 2004 23.05190592
Home 2004 22.14865963
Away 2005 23.2
Home 2005 22.31707317
Away 2006 22.47886179
Home 2006 21.96422764
Away 2007 21.25609756
Home 2007 20.7804878
Away 2008 21.41382114
Home 2008 20.67154472
Away 2009 21.32845528
Home 2009 20.38617886
Away 2010 21.08699187
Home 2010 20.33821138
Away 2011 19.98686869
Home 2011 19.14848485
Away 2012 20.14157852
Home 2012 19.54515867
Away 2013 21.00813008
Home 2013 20.39268293
Away 2014 20.88852459
Home 2014 20.35245902

[Crow]

Thanks. So Home teams always average less fouls called on them, perhaps a mix of winning more and getting slightly more favorable treatment. But the differential is usually bigger, so at the avg. foul differential is the culprit for this yr to yr home win% slippage.

Top 15 teams by overall record are winning 70.3% of home games compared to 71.5 for top 15 all last season. So most of the slippage in home win% is coming from the weak teams.

But last season the east won 44% and the west 70% at home so actually the west overall slipped by more.

Betting world data could share perspective on relative performance of favorites and underdogs at home overall, in close games and blowouts.

[Mike G]

About 8 teams have gotten more PF/G at home this year. I think that's a rather large number, compared to most years.
The 15-yr avg of those numbers BLI provided is .64 more PF/G on the road; this year, it's .54

Ranked by home court advantage (MOV at home -minus- MOV on the road), some other anomalies:

Code: Select all

HCA    team       movH   movA     W%H    W%A
10.5  New Orleans  6.4   -4.1    .706   .348
10.4  Oklahoma     6.9   -3.5    .632   .381
9.5   Golden St.  15.9    6.4    .944   .750
9.3   Washington   6.1   -3.2    .773   .579
9.3   Denver       2.9   -6.4    .571   .316
6.7   Memphis      7.4     .7    .800   .650
6.0   Portland     9.0    3.1    .818   .632
5.2   Phoenix      5.3     .1    .611   .542
4.9   LA Lakers   -3.7   -8.7    .286   .300 *
4.9 Philadelphia -10.3  -15.1    .158   .238 *
4.5   Toronto      7.2    2.6    .696   .588
4.2   Sacramento   -.3   -4.5    .417   .375
4.1   Dallas       8.1    4.0    .700   .667
3.8   Minnesota   -7.2  -11.1    .158   .200 *
3.7   San Antonio  6.1    2.4    .714   .524
3.6   Boston       -.4   -4.0    .409   .250
3.4   LAClippers   7.6    4.2    .708   .588
3.2   Cleveland    1.7   -1.6    .550   .476
3.0   Utah        -1.8   -4.8    .368   .318
1.7   Milwaukee    2.2     .6    .529   .522
1.6   New York    -8.4   -9.9    .150   .095
1.4   Houston      4.7    3.4    .667   .700 *
0.8   Indiana     -1.3   -2.1    .421   .304
0.7   Charlotte   -2.3   -3.1    .409   .368
0.3   Atlanta      6.9    6.5    .842   .773
0.3   Miami       -3.5   -3.8    .368   .524 *
-1.4   Orlando    -6.6   -5.2    .263   .400
-2.6   Chicago     1.5    4.2    .545   .750
-2.7   Brooklyn   -3.5    -.8    .364   .474
-3.1   Detroit    -3.0     .1    .286   .500

3.58   NBA        1.79  -1.79    .529   .471

* 5 teams -- LAL, Phl, Min, Hou, Mia -- have been worse on the road (in MOV) but have a better W%.