Baseball By The Numbers By Michael Salfino

March 23, 2006
Adjusting for Park Effects

A generation ago, cookie-cutter ballparks prevailed, largely neutralizing the impact on stats like average, runs scored and homers.

There were exceptions, of course. For example, many believe that former Red Sox OF and MVP Jim Rice does not belong in the Hall of Fame because Fenway Park in that era boosted scoring by about 20%. And Rice’s career home/road splits are telling (.320 average with 208 homers at home, .277 with 174 homers on the road).

Most are surprised by those splits because they assume that Fenway park increased homers more for righties due to that seemingly inviting Green Monster. But then, as now, Fenway’s main hitting benefit relates to batting average. The 10% gain for all batters turns the typical .275 hitter into a .303 hitter at home and a .289 hitter overall. In ’05, that Green Monster only increased right-handed power by an inconsequential 5% over the entire 81 home games.

Last year, there were just three other parks that bumped batting average by more than 5%: Coors (Rockies, 19%), Ameriquest (Rangers, 8%) and SBC (Giants, 9%).

Home run park effects are much more dramatic. But we need to differentiate the impact for right-handed and left-handed hitters (as the vast majority of homers are pulled).

Here are the best homer parks for righties, with the percentage indicating the difference between what the home team and opponents hit there versus on the road: Wrigley (Cubs, 56%), Minute Maid (Astros, 41%), U.S. Cellular (White Sox, 40%), Citizens Bank (Phillies, 20%), Bank One (Diamondbacks, 18%) and SkyDome (Blue Jays, 18%).

While the SkyDome slightly hurts lefthanded power hitters, Minute Maid is the unfriendliest homer park in all of baseball for lefties (minus 40%).

The best homer parks last year for lefites were Safeco (Mariners, 46%), Bank One (46%), Coors (45%), Angel Stadium (34%), Citizens (27%), Ameriquest (18%), U.S. Cellular (15%).

Of course, ballparks also decrease homers. For righties, the worst parks are Petco (Padres, minus 35%), Shea (Mets, minus 29%), Jacobs (Indians, minus 27%), Kauffman (Royals, minus 27%), Busch (Cardinals, minus 21%), Comerica (Tigers, minus 16%).

In addition to Minute Maid, the dead-ball era is back for lefties at Jacobs (minus 28%), Kauffman (minus 25%) and Busch (minus 20%).

Let’s look at some players who have switched parks and have the wind of these effects at their back or in their face in ’06.

Buy

Jacque Jones (OF, Cubs): The lefthanded-hitting Jones had only nine homer at the Metrodome last year. He gets a 25% boost by switching to Wrigley, so pencil him in for 25 trots.

Preston Wilson (OF, Astros): Wilson, a righty swinger, gets about a 50% boost in homers compared to last year (Coors/RFK). That alone should push him over 35 homers.

Chris Young (P, Padres): The 6-foot-10 righty moves from Texas and gets a minus 43% swing in runs, which would have lowered his overall ERA last year from 4.26 to 3.44.

Hold

Kenny Rogers (P, Rangers): Might be a late mixed-league option, as he is minus 32% by moving from Texas. While Rogers was lucky in having his defense convert balls in play into outs last year, expect that sub-4.00 ERA to hold.

Brad Wilkerson (OF/1B, Rangers): His homer total last year would have increased from 11 to only 14 last year adjusting only for park effects. So find another reason to boost this lefty’s blasts.

Sell

Adam Eaton (SP, Rangers): He’s going the wrong way (from Petco to Ameriquest). Last year, these park factors would have turned his overall 4.27 ERA to a pumpkin-like 5.06.