ESPN.com: Baseball [Print without images]

Saturday, December 3, 2011
Caught looking

By Peter Keating
ESPN The Magazine

 Toronto posted some very curious home run numbers in 2010.

This article appears in ESPN The Magazine's Dec. 12, 2011, "Interview Issue."

DID JOSE BAUTISTA deserve AL MVP honors? Maybe. But the Blue Jays slugger shouldn't be allowed to sidestep allegations that he and his team have used a relay system from beyond the field of play to steal signs.

In August, my former colleague Amy Nelson and I detailed the charges in The Mag: Members of an AL team said that in 2010, they saw a man dressed in white sitting in the centerfield seats in Toronto signaling pitches to Jays hitters. Shortly after our story came out, Bautista admitted that members of the White Sox bullpen had confronted him about alleged sign-stealing, but he denied the accusations. "This is bogus," Bautista said.

But the numbers behind the charges aren't so easily dismissed. In August, we found that the Blue Jays enjoyed a huge power boost from hitting at Rogers Centre in 2010, when they cracked an MLB-leading 257 home runs. Now that this season is in the books, we can make an even stronger case that something strange happened in Toronto.

Over the past two seasons, MLB teams have hit an average of 3.5 percent more homers at home than on the road. But where does normal homefield advantage end and something manufactured begin? To find out, we turn to a method presented by Colin Wyers of Baseball Prospectus. For every season, he analyzes every batter-pitcher confrontation in each stadium and compares the results to the outcomes we would expect given the players' individual statistics. Wyers essentially attributes the difference between what happened and what should have happened to the ballparks: If hitters at Wrigley Field crack more homers than their stats say they should have, that suggests it's the stadium talking. By adding up all these differences and throwing in a few extra mathematical steps to reduce statistical noise, Wyers can estimate the impact that every home field has on various stats each season. He calls these estimates "park factors."

As these park factors reveal, many stadiums strongly influence home run rates but typically affect home and visiting players similarly. In 2011, for example, Rockies hitters gained 7.2 home runs for every 100 balls they made contact with at Coors Field, while visiting hitters gained 6.4 homers.

Sometimes, however, home-team hitters gain a much bigger edge than their visitors. The most extreme cases since 1950: the 1951 and '54 New York Giants, the 1956 Reds, the 2005 Rangers ... and the 2010 Blue Jays. A season ago, in fact, Rogers didn't just boost the Jays hitters' HR/contact rate by 18.9 percentage points. Rogers also depressed the visiting hitters' rate by 2.3 points. That gap of 21.2 points, the third-largest gap found in any park since 1950, is enough to give a Jays hitter about 10 extra homers in a 550-AB season. The result is so extreme (4.4 standard deviations beyond the historical average, for you statisticians out there) that there was about a 1 in 148,000 chance of it happening randomly.

It's funny, though: In 2011, the Jays' power edge at Rogers persisted at a lower level through the first half of the season, then all but disappeared -- around the time that other teams started making news for changing up their signs in Toronto even with no men on base. By the end of the season, there was nearly zero difference between how Rogers affected home and visiting hitters.

To be sure, a whopping home-run-on-contact rate gap could be the result of a home team adapting to its environment successfully. And a fluctuating park factor could result from chance. Still, the numbers are odd enough that they deserve further investigation. But Bud Selig has let the matter slide. "We never received a formal complaint from any of our clubs regarding this," MLB spokesman Pat Courtney told The Mag.

Asked how many formal complaints from clubs MLB got about players named in the Mitchell Report, the commissioner's office declined to comment.

Peter Keating is senior writer and columnist for ESPN The Magazine. Follow The Mag on Twitter and like us on Facebook.