Stuckey: How Changes to Petco Park Are Affecting Padres Over/Unders

I wanted to explore a topic I haven't seen talked about enough in the baseball betting community: Petco Park. Most baseball bettors think of Petco Park as a pitcher's park. Even the most recreational bettors will tell you this fact but struggle to explain why. More advanced baseball bettors will quote the dimensions, San Diego's marine layer and the ocean wind.

Well, that all may be changing. Yes, Petco has historically been a hitter's nightmare, but the ball has started to carry much more over the past few seasons.

When I visited San Diego a few years ago, I spoke with a season ticket holder outside of Petco who told me about the park's newfound carry. But this is more than just anecdotal. The numbers back it up and more importantly, there are tangible reasons for the changes that bettors should know.

Let's start by looking at data over two separate time periods:

As you can see, the home run factor (which compares the home run rates of home vs. road games) has jumped significantly since 2005. In fact, Petco's home run rate has exceeded 0.95 in three of the past four seasons — something that never happened between its open in 2004 and 2014.

While that jump is certainly material and the relative nature of the measure captures overall changing home run rates over time, it's meaningless without an explanation. Like the old adage in the field of statistics, correlation does not imply causation. You could argue that randomness caused the  jump over the past few seasons.

The New Petco Park

However, I can counter with five specific reasons for the more hitter-friendly conditions over the past few seasons.

1. Petco's dimensions changed in 2013. The fences were brought in and lowered at various points. Most of the changes occurred in right field, which especially benefited left-handed hitters who historically loathed hitting in San Diego.
2. Additional renovations were completed ahead of the 2015 season. These changes occurred in left and center as the dimensions were once again made more conducive to hitters.
3. Not only were portions of the fence brought in and lowered, Petco also implemented a new state-of-the-art scoreboard in 2015. It was five-times larger than the previous scoreboard and the third-largest in MLB at the time.
4. Two new high-rise buildings were also constructed behind Petco.
5. Before the 2018 season, Petco also installed a new video board in right field.

The impact of bringing the fences in and lowering them at various points in both 2013 and 2015 is self-explanatory. The architectural changes (buildings, scoreboard) are less intuitive but they have altered the air flow and made it easier to see the ball.

And don't trust my word for it. Listen to Wil Myers, who has hit almost half (39) of his 82 homers at Petco Park since arriving in San Diego in 2015.

A Complete Total Flip

Okay, so batters are hitting more home runs at Petco Park. So, what? The real question is has the betting market properly adjusted to these changes. And the answer for the past four seasons has clearly been no. Just take a look at these drastic results of betting Petco overs before and after 2015 courtesy of our Bet Labs data.

Between 2005 and 2014, only the Mariners and Rays had worse home under results than the Padres. But since the beginning of the 2015 season, only the Reds have been a better home over team than San Diego. From a top-three under team at home to a top-two over team. That's a stunning turnaround which is illustrated best in the ROI in the above chart.

Lastly, just because the ball carries more than it used to in San Diego doesn't mean overs will continue to have success. While you certainly should be aware of these noteworthy park changes, oddsmakers and the market can adjust.

If, for example, over/unders of 7 start turning into 7.5 on a regular basis, the edge may disappear. (Please keep this in mind for any profitable historical trend or angle that you may stumble across in a fairly efficient market.)

Regardless, erase those Petco Park assumptions from your brain!