Wednesday, August 3, 2005 - Page updated at 12:00 AM

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Offensively, Safeco has a bad reputation

Special to The Seattle Times

You don't have to be a professional baseball researcher to know that batters who work for the Colorado Rockies get a giant boost in their offensive stats from playing half their games in Coors Field, and the Rockies' pitchers see their numbers equally devastated. Their park is the most run-enhancing one in the majors this year.

What's not as well known is that Safeco Field is the opposite extreme. Yes, everyone knows it's pitcher friendly, but the numbers declare it to be dead last in the majors for offense.

The numbers are called "Park Factors." There are many models for accounting for how a home ballpark affects the performance of its players. The one we cover here — Park Factor 100 (PF100) is the simplest. It works by measuring a ballpark's effect on the key objective of the game: runs.

Park Factor 100 compares the runs scored and allowed by a team and its opponents in games at home versus its games on the road. This neutralizes how good or bad a team's overall hitting and pitching are.

To calculate PF100 for the Mariners, use this formula:

Mariners runs scored in home games plus opponent runs scored in those games divided by Mariners runs scored in away games plus opponent runs scored in those games.

The result is a percentage. A park that has a PF100 of 122 percent for a season is one where teams have scored 22 percent more runs than they would in the league average of parks. A field that has a PF100 of 96 percent is one where teams have scored 4 percent fewer runs than they would in the league average of parks.

Here are the American League PF100s for this year:

Home park PF100
Texas Rangers 122%
Chicago White Sox 114%
Toronto Blue Jays 113%
Boston Red Sox 112%
Baltimore Orioles 108%
Minnesota Twins 105%
Oakland Athletics 101%
Los Angeles Angels 97%
Cleveland Indians 96%
Detroit Tigers 92%
New York Yankees 92%
Tampa Bay Devil Rays 91%
Kansas City Royals 91%
Seattle Mariners 83%

This year, Safeco's PF100 makes it the most extreme pitcher's park in the league.

Parks shift from year to year due to several factors. One constant, though, is that Safeco Field has consistently been the league's extreme run-destroyer, holding that end of the list in 2004, 2003 and 2002, as well.

A high or low PF100 isn't a bad or good thing. It's just the way a field affects the game and how batters' and pitchers' stats will look. Playing half their games in Safeco will make hitters look, in general, more anemic than they actually have been. Equally, it fluffs up, in general, the apparent performance of the M's pitchers.

I say "in general" because PF100 measures only the effect on the average hitter or pitcher. The reality is a lot more complicated. Many parks affect right-handed hitters differently from lefties. In Safeco, for example, it's easier than the league average for left-handed hitters to hit homers, and harder than average for right-handed hitters to knock one out.

Finally, note that park factors vary during the season. There's a lot more that affects how a park plays than how far away the fences are. Other factors include altitude (pitches break less and hit balls carry farther in thinner air), prevailing winds and temperature (warmer balls go greater distances). And in a park like Seattle's, whether the roof is open or closed makes a difference, and day and night effects are different. We'll explore that in later columns

When you look at PF100, it's surprising that Safeco Field hasn't become as notorious as Coors Field.

Jeff Angus writes on the new baseball statistics, describing what they reveal about the game and how that affects the Mariners. He is the author of "Management by Baseball" and of the Web log at Reach him at At 5 p.m. Monday, he'll read from his book at Elliott Bay Book Co.

Copyright © 2005 The Seattle Times Company


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