Home and Away Assists and Blocks

[Mike G]

I don't think much if anything on this subject survived the great evisceration. Here are the last 21 seasons' average home and away rates, and estimated 'extra' assists and blocks (per team) granted by home scorekeepers.

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yr     HAst%  AAst%  HBk%  ABk%  AsA/H BkA/H  xHAs xHBk
1991   .617   .581   6.5   5.6   .940   .852   62   35
1992   .613   .570   6.8   6.0   .929   .874   75   30
1993   .627   .588   6.5   5.6   .937   .861   67   31
1994   .637   .602   6.7   5.7   .944   .849   58   34
1995   .635   .594   6.7   6.0   .934   .881   65   25

1996   .631   .593   6.8   5.8   .939   .848   58   33
1997   .629   .592   6.6   5.7   .938   .844   56   31
1998   .631   .595   6.9   5.8   .941   .838   55   35
1999   .628   .585   6.8   5.9   .930   .846   60   30
2000   .626   .587   6.9   5.7   .938   .823   57   38

2001   .626   .571   7.1   6.0   .912   .837   81   37
2002   .622   .589   6.9   6.0   .946   .868   50   31
2003   .619   .583   6.7   5.7   .940   .851   53   34
2004   .619   .583   6.7   5.7   .940   .851   53   34
2005   .608   .576   6.5   5.6   .946   .874   48   27

2006   .587   .563   6.4   5.5   .958   .855   35   29
2007   .598   .566   6.2   5.4   .946   .870   48   26
2008   .599   .568   6.3   5.3   .945   .855   48   31
2009   .579   .551   6.4   5.5   .949   .869   43   28
2010   .578   .548   6.2   5.7   .944   .903   46   18
2011   .589   .566   6.5   5.5   .959   .839   36   33

Ast% = Ast/FG
Blk% = Blk/100 OppFGA
The A/H ratios may be thought of as the 'real' fraction of home Ast and Blk.

Home blocks generosity hit an alltime low in 2010, then shot back to near an all-time high this past season.
Home assist bias is less than half what it was in 2001.

[Mike G]

The 20 biggest home/away blocks ratios of these 21 years:

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tm     yr    HBk%  ABk%  BkH/A  HBlk  ABlk  xHBlk
Tor   1999   11.5   5.0   2.28   369   156   207
Den   2000   12.0   6.0   1.99   409   209   204
Tor   2000   10.6   5.3   2.02   366   178   184
Tor   2001   10.2   5.2   1.97   347   172   171
Den   2001   10.0   5.5   1.81   346   192   155

SAS   1996    9.9   5.9   1.68   332   205   134
NJN   1991   10.1   6.5   1.55   373   230   133
NJN   1992   10.4   6.8   1.54   373   242   130
Tor   1998   11.6   7.8   1.49   394   267   129
LAL   1995    9.8   6.2   1.59   344   217   127

tm     yr    HBk%  ABk%  BkH/A  HBlk  ABlk  xHBlk
Cle   1993    9.2   5.6   1.63   328   205   126
NJN   1994    9.8   6.4   1.54   353   226   124
Uta   1997    8.5   4.6   1.87   267   139   124
Den   1999    8.6   5.0   1.71   287   164   119
Cha   2010    8.6   5.0   1.71   283   164   117

Uta   2003    9.2   5.5   1.67   290   177   116
Uta   2004    9.2   5.5   1.67   290   177   116
NJN   1995    9.6   6.3   1.53   336   213   116
SAS   2001   10.1   6.9   1.48   346   230   112
Den   1994   11.4   8.2   1.39   398   287   111

Not quite 1/5 of teams have gotten fewer blocks at home; led by these teams:

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tm     yr   HBk%  ABk%  BkH/A  HBlk ABlk  xHBlk
Sea   1992   5.6   7.5   .75   193   254   -64
Mil   2000   4.8   6.4   .75   165   216   -55
Por   1997   5.9   7.6   .78   189   246   -53
Sea   1991   4.9   6.4   .77   164   217   -49
Por   2000   5.3   6.8   .78   172   224   -49

Por   2006   5.9   7.4   .80   187   247   -47
Mil   1996   4.0   5.5   .73   127   180   -46
Por   1995   6.5   7.9   .82   209   258   -46
Bos   2010   5.6   7.0   .80   176   226   -43
Atl   2001   5.2   6.5   .80   167   220   -43
Por   1998   6.5   7.8   .83   213   250   -43

I can only guess that some shotblockers on these teams were less popular at home than around the league in general.

[Crow]

This was one thread recovered that dealt with assists at player level:
http://sonicscentral.com/apbrmetrics/viewtopic.php?t=74

Another
http://sonicscentral.com/apbrmetrics/vi ... p?f=2&t=29

There might be others but it gets hard to find.

[Mike G]

2010-11 team home/away ratios, estimated 'extra' blocks and assists credited at home, ranked by the total (Ast+Blk) freebie count.

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xA+B   tm  HAst  AAst  HBlk  ABlk  xHAs xHBk  AFac   BFac
235   LAC   991   822   243   159  150   85   .917   .789
185   Cha   932   796   267   169   90   95   .948   .781
178   GSW  1019   828   215   191  151   28   .918   .932
160   SAS   988   848   211   161  114   46   .938   .877
148   Chi   952   875   276   192   64   84   .965   .821

145   Den   984   829   209   144   86   59   .952   .833
127   Cle   905   815   190   151   91   36   .947   .895
112   Okl   886   786   254   233   88   25   .948   .949
112   Was   838   754   273   229   68   44   .957   .913
107   Atl   966   836   171   170  105    1   .941   .996

106   LAL   945   856   239   183   50   56   .972   .867
105   NOH   898   793   196   164   71   34   .958   .905
101   Min   855   795   231   191   59   42   .964   .902
93    Det   928   802   179   149   64   29   .963   .912
88    Phl   965   896   194   162   56   33   .970   .908

xA+B   tm  HAst  AAst  HBlk  ABlk  xHAs xHBk  AFac   BFac
80    Tor   940   855   187   162   53   27   .971   .924
50    Orl   837   799   201   183   33   17   .980   .955
42    Mil   774   771   216   183   10   33   .994   .918
42    Bos  1005   917   180   166   28   13   .985   .962
25    Phx   965   980   195   163   -5   30  1.002   .917

20    Dal   988   966   186   166   -3   23  1.001   .934
15    NJN   871   852   203   183    1   13   .999   .965
8     Hou   968   987   201   170  -25   34  1.013   .909
-7    Sac   806   869   208   183  -39   32  1.023   .919
-9    Ind   815   796   244   213  -36   28  1.023   .939

-9    Mem   850   841   242   199  -55   46  1.033   .895
-37   Uta   946   975   260   225  -68   31  1.035   .936
-37   Por   877   859   166   192  -11  -26  1.006  1.073
-38   Mia   780   859   232   198  -72   34  1.044   .921
-74   NYK   875   882   221   253  -47  -27  1.027  1.057

These teams at the bottom toe the line against extravagant assists, blocks, or both. The negative totals suggest that league-wide, scorekeepers tend to be generous; and especially generous to the home teams.

The last 2 columns are factors that could be applied to the assist and block totals/rates of players for these teams. The blocks factor (BFac) accounts for opponent FGA, home and away; the assist factor (AFac) is based on team Ast/FG, home and away.

So any Clippers player could have his assists multiplied by .917 to get a better estimate of his real assist rate. Better yet, one can look up their individual home/away rates.
http://www.basketball-reference.com/pla ... lits/2011/

Blake Griffin had 188 assists at home, and just 124 on the road. Per minute, 48% more assist at home.
The Clipps, though, had 2.35% more FG at home; so Blake's real home inflation is only about +44%
The LAC team AFac (.917) times his 3.6 Ast/36 season rate = 3.3 Ast/36, roughly.
But his Away rate of 2.5 Ast/36 is even lower. The team average only gets us closer to the truth.
Griffin also had 50% more blocks at home (27 vs 18)

The correlation between AFac and BFac is .444

[Mike G]

Home blocks generosity hit an alltime low in 2010, then shot back to near an all-time high this past season.
Home assist bias is less than half what it was in 2001.

The 2010-11 league avg home/away for Ast/FG was 1.043
For Blk/OpFGA, the H/A ratio was 1.191 -- players were credited with blocks 19% more often at home.

How does this translate to playoffs?

This year's 16 playoff teams had regular season home/away ratio of 1.034 for Ast, and 1.159 for Blocks.
Then in playoffs -- unweighted by the games they played -- averages were 1.024 and 1.107 .
Home assist bias among playoff teams averaged just 71% of the regular season's, and blocks bias was just 67%.

But for total playoff Ast and FG, Blk and FGA -- which is to say, weighting by the number of games each team played -- the aggregate playoff assist bias was only 1.017 (.50 of RS), and blocks bias was 1.066 (.42 of RS).

There seem to be correlations between (a) holding down home scorekeeping bias and making the playoffs, and (b) holding down bias and going further in the playoffs.

[Mike G]

The 2010-11 playoff teams with their regular season and playoff games, home and away Ast% and Blk%, the H/A ratios, and 'extra' home assists (above and beyond road rates), here given as per-game.

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tm     G   HAs%  AAs%  HBk%  ABk%  AsH/A  BkH/A  xHAst  xHBlk
Dal   82   .64   .64   5.6   4.9   1.00   1.14    -.07    .57
Dal   21   .60   .57   5.9   4.7   1.05   1.25    1.00    .93

Mia   82   .52   .56   7.0   6.0    .92   1.17   -1.75    .83
Mia   21   .49   .52   7.8   8.0    .96    .98    -.77   -.10

Okl   82   .57   .52   7.5   6.8   1.11   1.11    2.14    .61
Okl   17   .51   .49  10.0   8.4   1.06   1.18    1.01   1.32

Chi   82   .62   .58   8.5   5.9   1.07   1.43    1.57   2.04
Chi   16   .57   .61   8.6   9.2    .94    .94   -1.53   -.49

tm     G   HAs%  AAs%  HBk%  ABk%  AsH/A  BkH/A  xHAst  xHBlk
Mem   82   .51   .55   7.5   6.1    .94   1.24   -1.35   1.13
Mem   13   .54   .49   7.0   8.1   1.08    .87    1.43   -.78

Atl   82   .64   .57   5.2   5.2   1.12   1.01    2.57    .03
Atl   12   .57   .53   5.7   6.9   1.08    .83    1.39   -.91

LAL   82   .59   .56   6.9   5.3   1.06   1.31    1.21   1.36
LAL   10   .55   .53   8.8   5.1   1.04   1.74     .68   2.81

Bos   82   .64   .63   5.6   5.2   1.03   1.08     .70    .32
Bos    9   .59   .59   5.6   5.3   1.01   1.06     .09    .22

tm     G   HAs%  AAs%  HBk%  ABk%  AsH/A  BkH/A  xHAst  xHBlk
NOH   82   .60   .55   6.3   5.2   1.09   1.21    1.73    .83
NOH    6   .65   .58   4.1   4.0   1.11   1.01    1.97    .04

Orl   82   .56   .54   6.1   5.6   1.04   1.09     .79    .42
Orl    6   .44   .49   4.0   6.4    .89    .63   -1.66  -1.77
                      
Por   82   .58   .59   5.3   6.2    .99    .86    -.27   -.64
Por    6   .47   .56   7.7   6.4    .85   1.20   -2.85    .96

SAS   82   .62   .55   6.1   4.8   1.13   1.28    2.77   1.12
SAS    6   .58   .49   6.2   8.6   1.19    .72    2.98  -1.95

tm     G   HAs%  AAs%  HBk%  ABk%  AsH/A  BkH/A  xHAst  xHBlk
Den   82   .60   .55   6.0   4.3   1.10   1.39    2.11   1.44
Den    5   .61   .50   6.3   3.3   1.21   1.89    2.60   1.89

Ind   82   .53   .55   7.1   6.3    .96   1.13    -.89    .68
Ind    5   .36   .57   7.1   6.9    .63   1.04   -5.39    .18

Phl   82   .61   .58   5.9   4.9   1.06   1.20    1.36    .79
Phl    5   .62   .59   5.7   4.0   1.04   1.44     .64   1.10 

NYK   82   .55   .57   6.5   7.3    .95    .89   -1.15   -.66
NYK    4   .59   .46   7.9   8.6   1.27    .92    3.96   -.54

tm     G    HAs%  AAs%  HBk%  ABk%  AsH/A  BkH/A  xHAst  xHBlk
allRS  82   .59   .57   6.4   5.6   1.034  1.159    .72    .68
allPO 10.1  .55   .54   6.8   6.5   1.017  1.066    .30    .23

A major disclaimer is in order: Because every playoff team has 1 to 4 specific opponents, their 'away' rates are not vs NBA average opponents (nor vs avg opponent scorekeepers).
Still, the league season and playoff averages may be relevant (bottom 2 lines).

[Mike G]

With 1/8 of this season played, every team has at least 2 games home and away.

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tm    hBk%   aBk%   A/HBk     hAs%   aAs%   A/HAs
Atl   .073   .054    .75      .638   .582    .91
Bos   .073   .083   1.14      .694   .634    .91
Cha   .080   .045    .56      .619   .523    .84
Chi   .124   .049    .39      .615   .639   1.04
Cle   .075   .075   1.00      .593   .573    .97

Dal   .032   .074   2.34      .667   .564    .85
Den   .070   .049    .71      .652   .555    .85
Det   .031   .046   1.49      .556   .576   1.04
GSW   .056   .044    .78      .590   .577    .98
Hou   .075   .036    .49      .588   .582    .99

Ind   .097   .044    .46      .467   .579   1.24
LAC   .056   .084   1.51      .632   .591    .93
LAL   .077   .063    .82      .633   .505    .80
Mem   .058   .054    .92      .434   .524   1.21
Mia   .049   .084   1.73      .620   .581    .94

Mil   .072   .039    .55      .633   .600    .95
Min   .047   .047    .99      .484   .563   1.16
NJN   .074   .036    .49      .578   .561    .97
NOH   .095   .036    .38      .526   .545   1.03
NYK   .080   .050    .63      .476   .623   1.31

Orl   .050   .048    .95      .570   .644   1.13
Phl   .095   .061    .64      .573   .571    .99
Phx   .050   .081   1.63      .603   .562    .93
Por   .081   .052    .64      .586   .609   1.04
Sac   .051   .062   1.23      .438   .379    .86

SAS   .048   .046    .96      .627   .547    .87
Okl   .082   .066    .81      .579   .489    .84
Tor   .079   .059    .75      .600   .695   1.16
Uta   .127   .068    .54      .557   .614   1.10
Was   .114   .077    .67      .455   .473   1.04

NBA   .072   .057    .789     .576   .569   .987

Assist bias is almost nil in the early going, while blocks are really happening at home.
In both cases, a seeming trend, from 2010 to 2011, to 2012.