Tuesday, June 14, 2011
Introducing HR/OFFB Park FactorsPosted by Jeffrey Gross at 1:03am
A couple of years ago, former THT writer Dan Turkenkopf tabulated an index of single-season (2009) and four-year home run per fly ball (HR/FB) park factors. I have griped plenty about using HR/FB rates over home run per outfield fly ball (HR/OFFB) rates in tabulating xFIP many times in the past, most recently last week, because HR/FB rates include pop-ups (IFFB), which can never be home runs. The data, over large samples, may be insignificant in difference overall, but why use bad data and skew the margins? It's like Fangraphs' incomprehensible decision to use strikeouts per at-bat (K/AB) instead of strikeouts per plate appearance (K/PA) to calculate strikeout percentage*. (Dave Cameron has indicated that recalibrating Fangraphs' database would likely be a cumbersome process.)
*Here are two examples why Fangraphs' K% calculations, done as K/AB, make no sense. First, assume player X has a particular K/PA in year N. In year N+1, he maintains the same K/PA rate, but increases his walk rate. Though his K/PA remains stable, Fangraphs would report his K% as having "increased," imparting negative stigma and poor analysis by persons who are not aware that K%, not on the same scale as BB% (calculated as BB/PA), does not per se indicate actual strikeout skill. Likewise, players with higher walk rates exhibit disproportionately high strikeout rates.
Ryan Howard, for example, has a career K% of 31.9 percent on Fangraphs, but has only struck out in 27.5 percent of his total plate appearances. For Howard, who strikes out a lot, this may not matter or make much of a difference if you analyze him, but for a player like Prince Fielder (career 22.1 percent K%), it does. Fielder has struck out in only 18.6 percent of his total plate appearances. On the surface, it would seem as though Brennan Boesch (20.4 percent K%) and Ryan Braun (20.5 percent K%) are "noticeably" better at avoiding strike three, but are in reality substantially the same, owning respective K/PA rates of 18.1 and 18.4 percent for their careers.
Other high walk "strikeout" sluggers, such as Geovany Soto, have K/PA rates that are lower than low-walk players with lower K% rates. Some say "well you can't strike out in a walk, so why use plate appearances in the denominator," but you also can't strike out in a hit or walk in a strikeout, and yet we accept plate appearances as the denominator for walk rate (BB%). Plus, just logically, shouldn't K% represent how likely a player is to strike out when he comes to the plate? Why make Shin-Shoo Choo's year-to-year K% like comparing apples to oranges because of a fluctuating walk rate?
Particularly where your data has an abnormal pop-up rate, HR/FB-tabulated xFIP loses a lot of its value. In fields like Oakland where there is a lot of foul territory, and in parks like Wrigley, where there is practically none, the differences in HR/FB and HR/OFFB rates might make a difference. The difference may be a couple of home runs at most (park factors only apply, in theory, in a half-step, as a player's expected number of home games is just 50 percent), but in a game of inches, such could affect Z-Scores, data distribution, etc. If memory served, HR/OFFB has also shown to be less volatile year-to-year than HR/FB.
Because I have such a penchant for HR/OFFB-based calculations, including them as a data point in my xWHIP Calculator, I asked a favor of Dan, who has in turn tabulated an index of HR/OFFB rates by ballpark using data from 2006-2009. We did not have the necessary 2010 data offhand to tabulate 2007-2010 rates, but hopefully this offseason we will be able to plug in 2008-2011 data for a fresher version of these numbers.
As with Dan's 2009 post on HR/FB park factors, certain parks have less data, are weighted similarly (but without the same old data to affect the weights), and may not be as reliable. The data below regards old Twins Stadium (the Metrodome), while the Mets' and the Yankees' Park Factors are from one season only. The Nationals' Park Factor also only uses two seasons worth of data, and is weighted at 5 and 3. All other parks feature four-year weighed factors of 5,3,2,1.
Without further ado, here is the goldmine of data you've probably always wanted, but never had (at least not that I was aware of) until now:
Team Park LG 4-Year HR/OFFB 4-Year HR/FB 2009 HR/OFFB 2009 HR/FB Angels Angel Stadium AL 102 124 96 110 Astros Minute Maid Park NL 110 111 108 104 Athletics McAfee Colisuem AL 92 91 92 95 Blue Jays Rogers Centre AL 107 110 108 105 Braves Turner Field NL 91 86 95 90 Brewers Miller Park NL 108 120 106 108 Cardinals Busch Stadium NL 76 68 84 86 Cubs Wrigley Field NL 104 102 103 97 Diamondbacks Chase Field NL 100 91 106 99 Dodgers Dodger Stadium NL 92 72 95 89 Giants Pacific Bell Park NL 97 102 95 104 Indians Jacobs Field AL 87 72 88 75 Mariners Safeco Park AL 92 83 96 95 Marlins Dolphins Stadium NL 108 126 99 109 Mets Citi Field NL 104 104 98 98 Nationals Nationals Stadium NL 91 95 92 91 Orioles Oriole Park at Camden Yards AL 113 108 115 109 Padres PETCO Park NL 79 79 75 73 Phillies Citizens Bank Park NL 93 111 94 109 Pirates PNC Park NL 93 100 94 105 Rays Tropicana Field AL 114 121 111 110 Rangers The Ballpark at Arlington AL 98 97 97 98 Red Sox Fenway Park AL 97 108 90 98 Reds Great American Ballpark NL 116 123 114 121 Rockies Coors Field NL 111 101 112 103 Royals Kaufman Stadium AL 86 84 78 73 Tigers Comerica Park AL 96 86 101 94 Twins (old) Metrodome AL 88 101 96 109 White Sox US Cellular Field AL 113 108 118 115 Yankees New Yankee Stadium AL 120 120 130 130
Or, alternatively, the parks ranked from most-to-least home run inflating per outfield fly:
Team Park LG 4-Year HR/OFFB Yankees New Yankee Stadium AL 120 Reds Great American Ballpark NL 116 Rays Tropicana Field AL 114 Orioles Oriole Park at Camden Yards AL 113 White Sox US Cellular Field AL 113 Rockies Coors Field NL 111 Astros Minute Maid Park NL 110 Brewers Miller Park NL 108 Marlins Dolphins Stadium NL 108 Blue Jays Rogers Centre AL 107 Cubs Wrigley Field NL 104 Mets Citi Field NL 104 Angels Angel Stadium AL 102 Diamondbacks Chase Field NL 100 Rangers The Ballpark at Arlington AL 98 Giants Pacific Bell Park NL 97 Red Sox Fenway Park AL 97 Tigers Comerica Park AL 96 Phillies Citizens Bank Park NL 93 Pirates PNC Park NL 93 Athletics McAfee Colisuem AL 92 Dodgers Dodger Stadium NL 92 Mariners Safeco Park AL 92 Braves Turner Field NL 91 Nationals Nationals Stadium NL 91 Twins Metrodome AL 88 Indians Jacobs Field AL 87 Royals Kaufman Stadium AL 86 Padres PETCO Park NL 79 Cardinals Busch Stadium NL 76
Thanks again to Dan Turkenkopf for crunching the numbers for me. As always, leave the love/hate in the comments below.
Jeffrey Gross is an attorney (and die-hard Cubs fan) who currently resides in the suburbs of Chicago. In addition to writing for The Hardball Times, he also writes about craft beer as part of a side project blog titled "saBEERmetrics." He previously worked for The Daily Illini and Northern Star newspapers as a film critic and sportswriter (respectively). You can reach him by email at saBEERmetrics AT gmail DOT com.