Petco Park Fences Are Moving In – But Will It Work As Planned?


There has been talk for years about moving in the fences, and with new ownership and a new philosophy comes real action.  Give them credit, action is good.  Construction plans are in place and details have been revealed about the projected dimension changes, including a move of the visitor bullpen.

September 8, 2012; San Diego, CA, USA; San Diego Padres third baseman Chase Headley (7) during his turn at bat in the first inning against the Arizona Diamondbacks at Petco Park. Mandatory Credit: Christopher Hanewinckel-US PRESSWIRE

Their goal is to spur more offense and generate more HRs, and to produce more fan excitement. But will it all work as planned? As the article from the Padre MLB site states, “you don’t need an MBA in Quantitative Analysis to know what you were seeing at Petco Park,” this fan begins to wonder if the opposite is true.  Perhaps the Padre management board would have been better off with an MBA on board to help complement their decision making.  While shorter ballpark dimensions will have a positive increase on HRs generated at Petco, it is the air density and proximity of the water that have a greater dampening effect on HRs, and thus cause the large home to road splits we have seen from the Padre hitters.Consider the following data, sourced from ESPN Padre Season Stats Splits, and also the following data, sourced from National Climatic Data Center, regarding historical averages for barometric pressure, from San Diego North Island Coronado.

As a fan, I wished I had better access to data, but for the purposes of discussion and to make a point, the above data suffices.  One can compare HRs per month by the Padres and compare that with air density or barometric pressure in San Diego close to the ballpark, month by month.

Month     P(inHg)      HRs


April           29.99             11

May            29.95             15

June           29.91             19

July            29.90             22

Aug            29.88             26

Sept           29.88             25

A regression does not imply full causality, and thus there are other factors that contribute to HRs outside of air pressure.  Nevertheless the reasoning is sound and holds its own against sensitivity analysis and the pattern can be seen.  When air density decreases, there is less content and “stuff” in the air, and the ball travels further because there is less friction.  Just like in Colorado, it is the altitude and air density that increase HRs over park dimensions, and just like in San Francisco, it is the proximity to the water and air density that decrease HRs over park dimensions, so it is at Petco Park and our air density and proximity to water that hurt our offense over park dimensions.

So what does this mean for Padre hitters?  Consider the case of our two main power threats, Chase Headley and Carlos Quentin.  Last season Chase had a fine first half, coupled with an extraordinary second half.  A lot of writers unfortunately choose to conflate analysis or reasons as to why Chase suddenly did better near the end of the seasons, such as seeing the ball better and taking it to the pitcher.  What they missed out on, was that almost all Padres hitters experienced power surges and increases to OPS late in the year.  It is my contention that it is the air density, which is related to temperature and humidity, that can change how Padre players hit and pitch at Petco Park.  Expect to see Chase struggle early again next year, and then catch fire as the season progresses.  Carlos Quentin, who was once an AL MVP candidate, consistently demonstrated higher OPS numbers than Chase.  Unfortunately, Carlos got hurt and worn down near the end of the year, and missed out on the late season HR party.  Expect next year to see Carlos be our best deep threat, with Chase right behind him given health and availability.