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07/11/2006 12:33 PM ET
Security Service Field: Context Matters


"For me context is the key - from that comes the understanding of everything". - painter Kenneth Noland

In June, Mike Claus wrote two fine articles under the banner "Understanding Stats" in which he delved into first hitting and then pitching statistics to explain the usefulness of metrics such as SLUG, OPS, WHIP, and GO/AO ratio. And while these metrics are indeed excellent for giving you a quick overview of just how productive a hitter has been or how effective a pitcher has performed, in their raw form they leave out a critical aspect that should interest Sky Sox fans as much as any other fans of professional baseball.

That aspect is the physical context in which the performance occurs.

The Sky Sox play their home games at Security Service field which was built in 1988 (then called Sky Sox Stadium), recently remodeled and is now a first class venue for minor league baseball which this author visits as often as possible. Security Service Field also has the distinction of course of being at the highest elevation (6,531 feet) of any North American professional baseball park. At that elevation, as with Coors Field in Denver but to a smaller degree since Coors is over 1,000 feet lower, the game literally takes on a different air.

At this higher elevation there are three primary affects. First and most obviously, a baseball travels farther when hit because of the thin air. Physicist Robert K. Adair who was once appointed "Physicist to the National League" estimated that a 400 foot fly ball at sea level would go 40 feet farther in Denver which of course means it would fly even farther in Colorado Springs. Second, storing baseballs in the low humidity environment has causes them both to shrink and lose weight, which conspire to make them fly even farther. Because of this, the Rockies have gone to storing baseballs in a locker dubbed "the humidor" where the humidity and temperature are controlled so as not to allow the balls to shrink and lose weight. And finally, on top of the first two effects, the thinner air means that pitchers have more difficulty getting their breaking ball to bite although their fastballs appear a bit livelier. As a result, it makes the job of Sky Sox pitching coach Chuck Kniffin especially trying.

Earlier this season Rockies directory of player development Marc Gustafson agreed that it takes a special pitching coach to help pitchers succeed in what is for the most part, an adverse environment.

"It's a valid point that the pitching coach for the Sky Sox might be the most important and demanding job in minor- league baseball. Most definitely pitching there prepares a pitcher for Coors Field. You have to have the mentality of a doctor. Pitchers have to learn to be tough- minded and to handle adversity."

So how does this relate to the statistics of Sky Sox players?

Simply put, since the environment is indeed a bit different at Security Service Field the performance of the players, and hence their statistics, will tend to reflect that difference.

Luckily, people who analyze baseball statistics have run across this phenomenon many times in the past. It turns out that it isn't only elevation that "distorts" a player's statistics. For example, it has long been understood and it seems intuitive that the Green Monster at Fenway Park, the short porch in right field and "death valley" in left-center at Yankee Stadium, and even the oval shaped Polo Grounds where the New York Giants played for many years have an effect on the number of doubles and homeruns hit in those parks which in turn effects scoring. That means that when you take a player and move him from one park to another, his skills might be the same from year to year but the park (the context) in which he plays will make his statistics appear different.

To correct for the context performance analysts created what are known as park factors. Basically, these are multipliers that take into account the mix of home and road parks a player performs in and can be used to adjust statistics for comparison. You can think of them as numbers that encapsulate the total effect of playing home games at a particular park which includes field conditions, weather, park configuration, and yes, even altitude. A park factor of 1.000 would be a perfectly neutral park that doesn't bias statistics either way while a park factor of greater than one indicates a hitter's park while a factor less than one indicates a pitcher's park. More granular park factors that take into account only homeruns or only doubles or triples can and are also calculated but we'll just stick to the total park factor here.

So if player a has an OPS of .850 but plays his home games in a park like Zephyr Field in New Orleans with a park factor of .907 (relative to the Pacific Coast League), one could adjust his OPS by dividing it by the park factor to give an adjusted OPS of .937. On the other hand if player B recorded an OPS of 1.027 but played for the Tucson Sidewinders at Tucson Electric Park (park factor 1.096), his adjusted OPS would also be .937. So while on the surface player A appears inferior to player B, by accounting for the context in which they play we can more correctly view player A's performance as on par with player B. The same can be done for a pitcher's Earned Run Average (ERA).

There are several ways in which park factors are calculated. At Baseball Prospectus we calculate park factors for every major and minor league team and publish them in our yearly annual. The method we use is to calculate a ratio of runs scored at each team's home park to runs scored in games on the road and then apply a weighted average over a number of seasons to help ensure that factors such as particularly strange weather one summer or a particular mix of players don't skew the numbers terribly.

As you can imagine, for the Sky Sox at Security Service Field the park factor is greater than one and in 2005 was 1.033, meaning that offensive output for Sky Sox players over the course of a season is inflated just over 3%. But even with the high elevation the Sky Sox park factor was only fifth in the PCL in 2005.

Las Vegas1.089
Salt Lake City1.081
Colorado Springs1.033
Des Moines1.003
Oklahoma City0.973
Round Rock0.957
New Orleans0.907

While on the surface this may seem a little strange, keep in mind that park factors are computed relative to the league and so it just happens that the PCL contains other cities at high elevation (Albuquerque 5,314 feet, Tucson 2,389 feet, Salt Lake City 4,330 feet, Las Vegas 2,178 feet,) and low humidity that offset some of the elevation at Security Service Field. In addition, park dimensions, field conditions, and configuration also play a large role in determining the park factor. Overall because of these parks the PCL is often viewed as a "hitter's league" relative to the other AAA league, the International League.

It turns out that in baseball, as with most things in life, context matters. And certainly context matters at Security Service Field as much as anywhere else.

This story was not subject to the approval of the National Association of Professional Baseball Leagues or its clubs.