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There's No Place Like Home...

HOUSTON - Wandy Rodriguez, shown here on Aug. 31, has pitched better at Minute Maid Park than on the road (Photo by Bob Levey/Getty Images).
HOUSTON - Wandy Rodriguez, shown here on Aug. 31, has pitched better at Minute Maid Park than on the road (Photo by Bob Levey/Getty Images).
Getty Images

Dave Cameron, at Fangraphs, tackled the issue of the Rockies' Carlos Gonzalez's home and road splits, sparking a debate  about how those splits should be considered in most valuable player consideration.   His article made me wonder about the Astros' home / road splits and what they might mean.

First, let me present Cameron's point.  He contends that the value of a run in a high scoring run environment is less than a low run context, because it takes more runs to win a game in the former environment.  Here is the gist of his argument:

If the Rockies need to score six runs at home in order to win, a home run – which has a league average run value of 1.4 runs – by Gonzalez gets them 23.3 percent of the way there. The Padres, for instance, only need to score four runs in order to win at home, so a home run at Petco by Adrian Gonzalez, worth the same 1.4 runs, gets them 35 percent of the way to their needed total. A run in San Diego, or anywhere really, is worth more than a run in Colorado because of the run environment.

The run environment context is one of the reasons that I always liked "Pitching Runs Created" as a measure of pitching performance: PRC recognizes that a "run saved" inherently has more value than a "run scored" because saving a run lowers the run environment and thereby increases the value of each run scored.  If a team wins a game by a 1-0 score, the value of a HR in that game is higher than a HR in a game won by a score of 7-3.  Maybe Cameron's argument is really just a restatement of the need to use park factors in making comparisons.  But there could be another issue raised by his argument which goes beyond park factors; suppose a team's pitchers are good at pitching a lot of low scoring games, does that mean the hits and walks of the batters on that team are also more valuable than they would be if the hitters were playing for the Pirates, whose pitchers give up over 5 runs per game?  What if the team's pitchers are much better at home, does that mean that hitters on the team with good home batting splits are worth more to the team than if they had even splits?  Obviously, park dimensions and other location factors, like wind and elevation, play a role. But sometimes park factors won't explain why batters or hitters are better or worse at home or on the road.

Think about the Astros this year.  The Astros' pitching staff is much better at home than on the road--despite the fact that Minute Maid Park is completely neutral (according to Baseball for pitching.  The Astros' pitchers have a 4.64 ERA on the road and a 3.43 ERA at home.  Astros' pitchers allow an OPS+ of 94 at home and 104 on the road.  Astros' pitchers allow a slugging percent of .425 on the road and .374 at home.  The K/BB rate for Astros pitchers at home is 10% higher than on the road.  Does this mean that the Astros' batters with strong home splits are more valuable to their team, because they are contributing more toward wins, given the pitchers' ability to lower the run context in Minute Maid Park?

The Astros' batters also exhibit better performance at home in MMP than on the road.  The Astros batting average, slugging, and OPS are significantly better at home.  Home vs. Road: BA .250/.245; SLG .379/.348  OPS .684/.650.  Interestingly, The Astros' superior offense at home hasn't resulted in scoring  more runs per game at home.  So far, the
Astros are scoring 3% more runs per game on the road than at home (3.69 at home; 3.81 on the road.)  This is surprising, since it indicates that the Astros are more effective at converting hits and baserunners into runs on the road, probably due to better performance on the road with runners in scoring position. 

If the Astros are scoring fewer runs per game at home, how does the team achieve a .522 Win% at home, compared to .437 on the road?  The answer has to be the team's superior pitching splits at home.  The Astros allow 1 less run per game at home than on the road (3.9 vs. 4.9).  This would suggest "yes" to my question: Astros' hitters with strong home splits are providing more value, given the context of the teams' strong pitching at home that produces lower scoring games.

The fact that the Astros hit better and pitch better at home is not unusual.  Most teams are better at home than on the road.  The Astros splits vs. National League team splits can be compared with the Baseball-Reference's tOPS+ stat, which compares OPS splits to the team's overall average (with 100=team average).  As shown below, the Astros' pitching home advantage is greater than for the NL generally, but the Astros batting home advantage is less than the typical NL
batting home advantage.

Home tOPS+ / Road tOPS+
Houston Astros  105/96
Natonal League  107/93
Houston Astros  89/110
National League  94/107

The tendency for NL teams to hit and pitch better at home, on average, indicates that the different is not totally due to the physical aspects of the ballpark. (The average ballpark factor is 100; so we expect a tOPS+ of 100 on average, if the ballpark characteristics are the only factor for home/road splits.)   We don't know whether the additional factors favoring home performance might be the player's reaction to the favorable crowd, knowledge of the home park,  preference for sleeping at home, etc.

These are the Astros batters who have posted a much higher OPS at home (based on tOPS+), with >100 indicating the home OPS relative to the player's overall OPS:

Batter/Total Plate Appearances/tOPS+
Wallace  (109 PA)  143
Pence  (571 PA)  130
Feliz  (304 PA)  123
Berkman  (358 PA)  121
Michaels (165 PA)   118
Keppinger (493 PA)  108
Lee (558 PA)  108

Micheal Bourn's tOPS+ is 100, meaning that his batting has been the same on the road and at home.  The tOPS+ at home for batters who have been better on the road:

Batter/Total Plate Appearances/tOPS+
Sanchez (212 PA)  47
C. Johnson  (283 PA)  77
Blum (198 PA)  80
Manzella (258 PA)  86
Castro (179 PA)  89

Obviously there are some sample size questions with using splits for players who don't have a lot of plate appearances.  Wallace is the most home-oriented player, based on the charts above, but he barely exceeded the 100 PA threshold I used.  Given Wallace's total plate appearances and sparse hits overall, I doubt that this split indicates much really.  Is there a pattern for the remaining players?

  The sample sizes are smaller with the young players, but (setting aside Wallace) it is interesting that the younger players tend to post a higher OPS on the road, and the veteran players (with the exception of Blum) tend to post a higher OPS at home.  Again, maybe this is just an aberration.  But perhaps the veteran hitters have had more time to gain a comfort level at home, learning how to match their abilities to the ballpark.  Two of the Astros hitters with large differences between home and road OPS, Carlos Lee and Hunter Pence, have hit more HRs at Minute Maid Park this year than on the road (12 of 19 for Lee and 13 of 23 for Pence); and both Lee and Pence are prone to hit their home runs to LF, which is MMP's sweet spot for homers. 

Next, let take a brief look at starting pitchers. Wandy Rodriguez is well known for favorable home splits over his career.  And 2010 is no exception.  But he isn't alone.  This year the majority of Astros' starters were tougher on hitters in Minute Maid Park, compared to their overall pitching.  I show tOPS+ allowed for the starters at Minute Maid Park below, and in the case of pitchers, a tOPS+ below 100 indicates a favorable performance split.  For Roy Oswalt and J.A. Happ, the chart utilizes their splits for Minute Maid Park (rather than "home") because the mid-season trade confuses the home and road numbers. 

tOPS+ allowed
(In order of most favorable MMP split)

Happ   52
Wandy  70
Paulino  85
Norris  90
Myer  106
Oswalt 118

Although Happ's MMP performances are a small sample, can we speculate on why the two lefthanders in the rotation have the most pronounced splits for pitching at MMP?  Conventional thinking is that lefthanded pitchers are vulnerable at MMP due to the short porch in LF.  Maybe righthand hitters become overly anxious to hit pitches into the Boxes when they face a lefthanded starter in MMP.   Perhaps good lefthanded pitchers learn how to induce flyballs to the expansive CF.  Andy Pettitte, another pretty good LHP, has a career tOPS+ of 88 in MMP. 

The young righthand pitchers Paulno and Norris pitch better at MMP; watching Norris and Paulino this year, that isn't really surprising, since both guy seems more confident at home.  Both of the grizzled veteran RHPs, Oswalt and Myer, were road warriors this year, pitching better on the road than at MMP.  For Oswalt, this split is unusual, since he has pitched so well at MMP over his carer, with a career tOPS+ at home of 88.

So, do you see any surprises in th home/road splits for the Astros this year?  Do you buy into the argument that Astros' batters who hit better at MMP had more value to the Astros this year because of the overall lower runs allowed by Astros' pitchers at MMP?