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# The Changing Effects of Petco Park

Jeff Sullivan’s recent enjoyable trot through San Diego Padres statistics and history led to a number of commentors thinking about San Diego’s park factors. The Padres changed the outfield dimensions of Petco Park in the off-season, and since park factors are backwards looking and rely on multiple years of data, changing dimensions can throw a bit of a monkey wrench into the calculations. So, it’s possible that our park factors are now somewhat behind the times, and we need to keep this in mind when looking at the park adjusted numbers (such as wRC+, ERA-/FIP-/xFIP-, WAR, etc…) for San Diego players, both hitters and pitchers.

It’s not quite so simple as noting that the changing dimensions have made the old park factors useless, however. Moving in the fences helps home runs, yes. This is undeniable. But it also can decrease triples and doubles, as well as effect the more odd elements of park factors, such as walk-rates, strikeout rates and pop-up rates.

It’s too early in the season to construct terribly useful park factors for the new dimensions, but we can do some harmless back-of-the-napkin mathematics to at least determine if the recent numbers suggest at least the early signs of serious run environment changes.

Below are the extra base hit rates (per PA) for Petco Park stretching back to 2005:

Doubles and triples are down, and home runs are way up. For greater specificity, we can see those same numbers in table form:

Season 1B% 2B% 3B% HR%
2006 15% 3.87% 0.72% 2.46%
2007 14% 4.18% 0.63% 2.39%
2008 15% 3.81% 0.49% 2.15%
2009 13% 3.51% 0.53% 2.02%
2010 15% 3.36% 0.47% 1.96%
2011 14% 3.77% 0.78% 1.56%
2012 15% 4.48% 0.84% 1.57%
2013 15% 3.82% 0.37% 2.40%

Does anyone else find it curious the 2013 doubles rate compares favorably to the same rate from 2008 through 2010? And the home run rate matches the unusual 2006 blip? This is why most (good) park factors include multiple years — in an effort to avoid catching weird blips — and include adjustments to reflect league-wide run environments. Odds are, some of the changes here may be reflections of the Padres personnel and the ever-morphing strengths of the NL West as much they reflect the effects of the park itself.

So has Petco Park changed appreciably this season? We can’t say. What we can say: Doubles have decreased 0.42% since the 2005-2012 period, triples have decreased 0.22% and homers have increased 0.72%.

If we convert that to run values (using 2013 adjusted constants, i.e. divide the constants by the wOBA scale):

#### Debit

2B: 0.0042 x (1.262/1.262) = 0.42% fewer runs per PA
3B: 0.0022 x (1.608/1.262) = 0.28% fewer runs per PA

#### Credit

HR: 0.0072 x (2.080/1.262) = 1.19% more runs per PA

That’s a 0.49% increase run value per PA. In (3 x 9 PA) 27 PA of a game, that’s an increase of 0.135 runs. In about 7 games, they are scoring an extra run; that’s an extra run per week. So we can say this: More game-context-neutral offense has thus far occurred at Petco Park.

I say that so awkwardly on purpose. I do not want to suggest these home park numbers will continue on their present pace without any further fluctuation. What he have is 36 games, and that’s all we can really speak about with any authority.

Another question we may also want to address: how has the Padres run scoring / run prevention changed? Well, with the Padres hitters, we see the same pattern of decreased doubles and triples, increased homers:

And though the doubles rate decreased well beneath 2013 levels, it nearly equals the 2006-2011 levels. The homer rate is considerably higher than the preceding years, but is not much above the Padres’ late “steroid era” years.

And with the pitchers, the DIPS numbers are steady with the essential, weighty exception of their home run rate (NOTE: I’ve removed IBB from the BB-rate):

That is a 1.97% HR-rate ballooning to a 3.09% HR-rate. It’s fair to say the pitching staff is a collection of non-studdish hurlers, but regardless of their mediocrity, they are maintaining nearly identical strikeout rates and walk rates with respect to recent rosters.

Is Petco Park haunted by its former dimensions? Yes, and we should keep that in mind when looking at the Padres park adjusted numbers. The Padres pitchers might not be quite as bad as those numbers make them look, since Petco probably isn’t quite as helpful to hurlers as it used to be. However we will need more time before we can measure the magnitude of these changes over the long term, and it is important to remember that changing the dimensions doesn’t turn a pitcher’s paradise into a hitte’s haven overnight.