Park it Here

Dave Paisley

What's a park factor? It's basically the effect that playing in a particular ballpark has on any factor in the game of baseball. Typically, however, the term is used to define the park's effect on runs scored.

Take Coors Field, for example. The Rockies scored 526 runs in their games at Coors, while their opponents scored 505 in those same games. Send the Rockies on the road, though, and in about the same number of games the Rockies scored a mere 300 runs, while their opponents scored 350. So that's 1031 runs in Coors, versus 650 at other ballparks, by essentially the same players.

Park Factor is the result of the runs scored in the games at that park (by all teams) divided by the runs scored in the road games of the team that plays its home games at the park in question. Then, we multiply the result by 100. Hey, even statheads don't like decimals at least some of the time. So the Coors Field park factor is:

(526+505) / (300+350) * 100 = 159

A neutral park would have a factor of 100, so by this measure Coors is most definitely a hitter's park.

However, runs scored is a poor measure of the way ballparks affect the game. Sure, runs determine the winner of a game, but I'd much rather take a deeper look at home and road effects based on OPS (on base percentage plus slugging average).

The most common use of park factors is to evaluate players across teams. Remember the fuss last year when Mike Piazza and Larry Walker were competing for the NL MVP? Walker played in Coors, where it was child's play to score runs, while Piazza played in LA, where it is about as difficult as possible. The MVP voters sure didn't take any of that into account, but you should. This year the player who may benefit most is Juan Gonzalez. But I'm getting ahead of myself.

Here are the numbers for the American league this year. I've included the run-based park factors for comparison. Note that the OPS-based factors don't vary as much from the 100 mean.
 
 

Team	Team Home OPS	Team Road OPS	Opponent Home OPS	Opponent Road OPS	OPS Park Factor	Runs Scored Park Factor
Indians	.833	.758	.794	.747	108	117
Rangers	.856	.781	.809	.774	107	115
Red Sox	.836	.786	.724	.723	103	100
Royals	.733	.715	.809	.781	103	110
Twins	.740	.695	.781	.791	102	100
White Sox	.822	.745	.778	.824	102	101
Devil Rays	.705	.706	.766	.746	101	109
Mariners	.831	.793	.781	.803	101	101
Tigers	.735	.742	.796	.779	101	103
Blue Jays	.815	.762	.704	.789	98	101
Yankees	.844	.806	.661	.738	97	94
Angels	.720	.779	.754	.779	95	93
Orioles	.792	.796	.721	.804	95	89
Athletics	.720	.749	.743	.822	93	85
Average	.784	.758	.759	.779

 

There are only two ballparks that have an OPS park factor higher than 105: Cleveland's Jacobs Field and Texas' Ballpark in Arlington. These are widely regarded as good hitter's parks, and so the numbers show. It also means that it was much easier for Juan Gonzalez to drive in all those runs in Texas than most other places. At the other end of the scale, only the Oakland Coliseum is more than 5% below the mean.

There are some anomalies between the OPS Park Factor and the Runs Scored Park Factor. Note that Tropicana Field in Tampa Bay is very close to even in OPS, but is 9% over on runs scored. As it's the park's first year, it's tough to draw any serious conclusions from that. We'll keep an eye on it, though.

You can also see that Kansas City's Kauffman Stadium and Fenway Park in Boston both have OPS Park Factors of 103, but the runs scored results are quite different. In Fenway, that 103 factor on OPS only resulted in neutral, league-average run scoring, while in Kauffman, it led to 10% more runs on average. That's the kind of random variation we can expect in run scoring, given the same basic hitting (i.e. OPS).

That's a basic look at park factors for now, but in my next article I'll take a look at which parks help the home/road advantage. Which team takes the biggest advantage of its home park? Which parks are hell to play in for the opposition?

I'll even get around to the NL eventually. And then there are year-to-year park factors. How do they change?

You'll find out soon...

Dave Paisley was discovered to have feet exactly twelve inches long, and is currently employed pacing off home run distances at Camden Yards. Tell him not to get those plates anywhere near my foot-long dog at drdjp@strikethree.com.

 

about the author