September 17, 2010

Checking the Numbers

CarGo on the Road

by Eric Seidman

It isn’t exactly breaking news that Carlos Gonzalez of the Rockies is having a fantastic season. Entering Thursday’s action, his .341 batting average topped the National League, as did his .612 slugging percentage, 182 hits, 106 RBI, 100 runs, and 326 total bases. Add in 23 stolen bases, a solid defensive reputation, and the fact that he is still the most likely candidate to achieve the Triple Crown, and it is very safe to say that he has soared far beyond reasonable expectations entering the year. PECOTA’s 90^th- percentile foresaw a .312/.386/.550 slash line, which he has surpassed, even if his long-term rate of reaching base is likely to be called into question.

Gonzalez has also made plenty of recent headlines for a different aspect of his offensive production, in that most of it has come in the friendly confines of Coors Field. In 305 plate appearances at home, Gonzalez is hitting an absolutely gaudy .392/.439/.766, with 25 of his 32 home runs and a 1.185 Raw True Average. In 271 trips to the dish on the road, his numbers are much more pedestrian: a .288/.310/.450 slash line with just seven home runs, and a .766 Raw TAv. This season, he is the greatest hitter of all time while at home, and Alex Gonzalez on the road.

To some, this isn’t a big deal. After all, players are expected to perform better at home than on the road. To others, like a Chipper Jones who is likely still upset that the Coors-infused Matt Holliday beat him out for the 2007 batting title, the vast differential in performance at home and on the road is enough to invalidate MVP credentials. I am not positive where I stand in this debate, though I do know that a difference of 419 points in Raw TAv between production at home and on the road is eye-popping and worthy of further investigation. Today, we’ll take a look at the biggest and smallest home and road splits in recent memory, and discuss the split in general.

Home/Road Splits Background

It is common for players to produce better numbers at home than on the road. From 1974-2009, the average player has posted a .740 Raw TAv on the road, and a .769 clip at home. Home-field advantages exist for teams in the wins column, but those wins are the byproduct of individual accomplishments from the players themselves. With platoon splits, the advantages are more readily understandable: batters perform better against opposite-handed pitching due to seeing the ball from a better angle. With home/road splits, the advantages are evident but tougher to explain. It isn’t terribly clear if the advantages are derived psychologically, like getting amped when the crowd goes wild, or environmentally, such as when a player feels comfortable in his home surroundings rather than living out of a suitcase. Another advantage could simply come from knowing the stadium.

In the case of Coors Field, the advantage has always involved altitude. The stadium is a mile above sea level, and visiting teams may have trouble adjusting over a short series. Rockies players, having spent the majority of their time in or around the stadium, will be better-equipped to handle the environmental factors. Additionally, the stadium has a notoriously high run environment; runs are expected to be scored, and it is expected that batters will post solid numbers in Colorado. For most of the stadium’s existence the inflated run environment was due to dry air and the effects it had on the baseball. To that end, the Rockies began storing balls in a humidor to lessen the effect.

Getting back to the averages at home and on the road, the split over the last three and a half decades has been right around 30 points of Raw TAv. By restricting the sample to anyone with 175 plate appearances both at home and on the road in a given season, the numbers increase to .778 on the road and .809 at home. Either way, the split remains right around 30 points, or well, well below the differential on display from Gonzalez.

The standard deviation of Raw TAv splits in this sample is .112, indicating that approximately two-thirds of players are expected to post a split somewhere between 82 points worse on the road and 142 points better at home. With a split of 419 points, Gonzalez is currently more than three standard deviations from the mean, a threshold supposed to encompass all but 0.3 percent of the population. Outlier much?

One issue I have always had with the valuation of players based on splits is that most of those doing the analyses fail to make the appropriate comparisons. The standard article will compare Matt Holliday’s production at home to his own production on the road, and upon seeing a huge split, the analyst will write the performance off. The same type of analysis usually persists in articles claiming Ryan Howard should be a platoon player; of course he has a huge split when compared to himself, but that isn’t entirely relevant.

The appropriate comparison is of the player’s split half to the league split-half. Gonzalez has a huge split here, but he is still essentially average on the road, just like Holliday was average or above on the road, and just like Howard is about average in the context of lefty-on-lefty matchups. Yes, the bulk of Gonzalez’s damage is done on his home turf, but he is only bad on the road when compared to himself, which is not a comparison we want to be making when trying to value productivity in a split. In fact, if you walk away with nothing else from this article, leave with the understanding that any article that discusses splits but does not compare the performance of the individual to that of the league is an incomplete article.

Where Does CarGo’s Split Rank?

With my rant out of the way, where does Gonzalez’s split rank all-time? Since 1974 and amongst those with 175 or more plate appearances both at home and on the road in the same season, here are the largest Raw TAv splits:

Name	Year	Raw TAv-H	Raw TAv-R	Split
Jesse Barfield	1983	1.031	.563	.468
Larry Walker	1999	1.359	.898	.461
Vinny Castilla	1995	1.133	.679	.454
Oscar Gamble	1976	.978	.547	.431
Justin Upton	2008	1.025	.599	.426
Gary Matthews	1977	1.012	.588	.424
Eric Young	1996	1.020	.599	.421
Tom Brunansky	1990	.993	.578	.415
Jeff Cirillo	2000	1.070	.658	.412
Bill Buckner	1977	.958	.556	.402

I can’t say that I am shocked to see both Larry Walker and Vinny Castilla on this list, as both were members of the Rockies in the listed seasons. Additionally, Eric Young was on the Rockies in 1996, and Jeff Cirillo played for them in the 2000 season. Everyone else produced their massive split without the aid of Coors Field, but it is in no way surprising that four of the biggest splits over the last 35 seasons came from Rockies players. Gonzalez, at .419, would rank as the eighth-largest split, which is a bit hard to comprehend given how extreme his split seems; it’s frankly hard to imagine someone outdoing him in this regard. These were also the only seasons with splits of 400 or more points in favor of the home stadium.

There were actually two seasons in which players performed 400 points better on the road, for oddity’s sake: Glenn Davis in 1990 (1.091 on the road, .683 at home), and Ryan Thompson in 1994 (.954 on the road, .527 at home). If you don’t remember Thompson, don’t worry, I didn’t either, but he managed to hit .243/.301/.433 over 1,385 PAs from 1992-2000. Of the roughly 6,700 player seasons in the sample, over 4,000 performed better at home, confirming the home-field advantage idea in addition to the Raw TAv average nearly 30 points greater.

The Anti-CarGo’s

Which players have had the lowest single-season splits in this regard? Has anyone ever been even to the third decimal? Maybe not so surprisingly, but yes, 27 different players that met the 175 plate appearances criteria fit this description. The 10 with the highest total of plate appearances are tabled below:

Name	Year	Raw TAv-H	Raw TAv-R	Split
Doug Glanville	2000	.699	.699	.000
David Ortiz	2006	1.027	1.027	.000
Vladimir Guerrero	2004	.985	.985	.000
Robin Yount	1983	.892	.892	.000
Dwight Evans	1979	.768	.768	.000
Keith Hernandez	1977	.845	.845	.000
Scott Hatteberg	2004	.805	.805	.000
Ryan Klesko	2002	.923	.923	.000
Chris Speier	1977	.678	.678	.000
Rick Manning	1976	.747	.747	.000

This table was admittedly more anecdotal than anything else, since it is tough to imagine players performing identically at home and on the road in the same season. Granted, if we extended the numbers to an additional decimal place the list would be much shorter, but don’t ruin my nerdy fun. So there you have it: Gonzalez has a mighty large split, but it isn’t the biggest of all time, and would in fact rank eighth were the season to end today. It is tough to imagine him performing even better at home and relatively worse on the road in order to overtake Jesse Barfield for the top spot, but this has been a fairly improbable season for the twice-traded prospect to begin with.

Eric Seidman is an author of Baseball Prospectus. 
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