Do Nick Markakis and Adam Jones play worse defense when they play at home? Are there park effects at work?

Gordon Gray, a Bill James Online subscriber, pointed out a discussion going on about these questions. Both Markakis and Jones have shown much worse range at home than on the road. Using the Plus/Minus System which measures plays made compared to an average center fielder, Jones has been a pretty average center fielder on the road making a total of just 4 fewer plays than an average center fielder in four years. But for some reason, at Camden Yards he's had trouble. He has made 20 fewer plays patrolling center field at home in the same four years.

Markakis has an even more pronounced home/road split playing right field. In his six years he is slightly above average on the road (+7 plays), but -29 at home. Here are the year-by-year numbers:

 

 

 

Jones has been better on the road three out of his four years, while Markakis has five out of six seasons with better road plus/minus numbers (counting 2011 as even).

The UZR system, which also relies on the detailed batted ball tracking information from Baseball Info Solutions, shows a similar result.

Did Jones and Markakis really perform better on the road or is there a possible measurement bias going on?

Here are my thoughts:

1) The most important park effect about Camden Yards is the 25-foot wall in right field. That park effect is eliminated in the Plus/Minus System (and the UZR system, as I understand it) by excluding any batted ball that is unfieldable because it hit high off the wall. Based on some preliminary analysis about park effects that we've done, we're not seeing anything else of note.

2) Jones and Markakis have played a substantial number of innings at Camden Yards (about 6700). Having made 52 more plays on the road than at home is significant. But if you look at all other Orioles outfielders who have played in Camden, in about twice as many innings, you don't have the same effect. All other Orioles outfielders in Camden Yards since 2003 have made 1 fewer play than average at home, and 8 fewer plays on the road. It's as we would expect for these outfielders, they are about the same at home and on the road.

3) The Plus/Minus System is an objective system that is simply saying Jones and Markakis have made plays on the road that they haven't made at home. That's all there is to it. That's my guess anyway; I think we'll need to do more research on this. I see it as more of a statistical anomaly than anything else. An example of this is David Ortiz from 2004 through 2006. He led Major League Baseball in road home runs every one of those years, hitting 24 more home runs on the road than at home. For the rest of his career in Boston his home-road totals are basically even.

 

We'll take a closer look at park effects in The Fielding Bible-Volume III coming out in a couple of months.