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Can We Quantify the “Marine Air Effect” at Safeco?

With the fences at Safeco Field moving in for the 2013 season, and the Mariners moving away from a defensive heavy approach to one that relies more on the home run, we expect to see more offense in Safeco, instead of the near unprecedented offensive black hole that Seattle was in 2012. Of course, while the Mariners have done their in-house studies as to how much this should improve offense, we also have to take into account the environment. A 400 foot fence in Colorado is not going to play the same as a 400 foot fence in Minnesota. In Seattle, there is the famous “marine air effect” that many people believe drives down offense, perhaps even more than the fences themselves. This is why some people don’t even trust the spray charts from previous teams when they come to Seattle, as they don’t believe the ball will travel as far. I wanted to see if we could quantify “the marine air affect”, using Baseball Heat Maps’ (.com) batted ball distances (on everything but bunts, which I removed).

Since Pitch F/X data started in 2007, I looked at the Mariners 2008-2012 rosters, looking for both pitchers and hitters that played significant time (I didn’t use a hard cut-off, but something like 200 plate appearances or 50 innings) for both the Mariners and some other MLB team in the Pitch F/X era. Since we can’t really break down home/road splits (we could manually, using game logs etc., but it would take an incredibly long amount of time for 51 players profiled below), we have to look at just the entire time they with the Mariners versus the other team. I split the data into pitchers and hitters (and before and after), but you should be able to click on the labelled sheets.


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As we can see, the variation between hitters does suggest that there is a slight effect on batted balls for hitters playing for the Mariners versus when they played for other teams. For pitchers, there was no real reason to think that they benefited from Safeco when it came to actual batted ball distance, meaning the ball seemed to travel normally. Of course, there are many variables that we didn’t account for, like aging curves, home/road splits, and there is a bias on ground-balls (since it doesn’t use Hit F/X, as that is not publicly available. My understanding is that ground-balls are measured when they are picked up, so a weak ground-ball that gets through may go 200 feet, even though it wasn’t hit as hard. Perhaps zeroing out ground-balls would be helpful in future study). With that said, this data doesn’t give us much reason to believe that the ball travels further (or obviously less) on average for the Mariners than any other team. How Safeco plays in 2013 may give us a better idea (especially since only two players played for the Mariners in 2012, which was the most extreme year).