As most of you are probably aware, player pages now feature splits. As such, we’re beginning a splits blitz which should educate our readers as to the many different usages of the newest toy. Home and road splits are probably the most commonly used and misused of all splits. Here I would like to show why just using career home/road splits to evaluate a batter isn’t a good idea.
A quick Google search of Matt Holliday + home/road splits brings back multiple results from this very chunk of the internet. For his career, Holliday has hit .351/.420/.632 at home and .284/.353/.455 on the road in 1,860 and 1,778 plate appearances apiece. It’s fair to say that he has performed better at home. Holliday has spent the majority of his career – read: every season but his last – playing home games inside of Coors Field.
That factoid helps explain some of the difference between his .442 home wOBA and .353 road wOBA, but not all. Far too often folks point out a player hitting worse on the road as an indictment on his talent, or as a doubt in his ability. The reality is that most players hit worse on the road. In 2009, the average major leaguer hit .267/.340/.430 at home and .258/.326/.406 on the road. The exact reasoning can be debated for eons; the point is the home field advantage does exist and Holliday was no exception to the rule:
Home: 8.9% BB, 17.1% SO, .281 ISO, .378 BABIP, 20.4% HR/FB, .442 wOBA
Away: 8.9% BB, 20.4% SO, .171 ISO, .329 BABIP, 12.3% HR/FB, .353 wOBA
Leading up to his trade, people referenced the career numbers – in part as an adjustment to the small sample sizes naturally associated by slicing and dicing an already small dataset. In theory, 1,000 plate appearances over five years is worth more than 600 over three, but when dealing with past data and attempting to find the true talent level of a player, we have to weigh the most recent data the heaviest, something lost in this method.
The other big issue was that people took the road numbers as gospel, applying no adjustments or considerations to the numbers and completely ignoring obvious factors. For instance, Holliday’s road numbers excluded Coors. Meanwhile every other National League hitter would have those numbers included in their road totals. That means Holliday’s road numbers were naturally deflated just based on the ballparks he batted in.
Just using his career numbers, nobody would’ve predicted that Holliday could succeed to the tune of a .412 home wOBA in another environment, or that he would post a .367 road wOBA. That’s not to say that either of those numbers are his true talent levels, either. It is to say that while understanding park factors and how particular parks can affect batters (and pitchers) is important, that simply looking at career home/road splits as the gospel is not the best way to evaluate whether a batter is a figment of the park’s construction or simply behaving like most major leaguers.
I would recommend simply allowing the built-in park adjustments within projection systems do the math for you while exercising common sense in extreme cases.
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