Dave Cameron, at Fangraphs, tackled the issue of the Rockies' Carlos Gonzalez's home and road splits, sparking a debate about how those splits should be considered in most valuable player consideration. His article made me wonder about the Astros' home / road splits and what they might mean.
First, let me present Cameron's point. He contends that the value of a run in a high scoring run environment is less than a low run context, because it takes more runs to win a game in the former environment. Here is the gist of his argument:
If the Rockies need to score six runs at home in order to win, a home run – which has a league average run value of 1.4 runs – by Gonzalez gets them 23.3 percent of the way there. The Padres, for instance, only need to score four runs in order to win at home, so a home run at Petco by Adrian Gonzalez, worth the same 1.4 runs, gets them 35 percent of the way to their needed total. A run in San Diego, or anywhere really, is worth more than a run in Colorado because of the run environment.
The run environment context is one of the reasons that I always liked "Pitching Runs Created" as a measure of pitching performance: PRC recognizes that a "run saved" inherently has more value than a "run scored" because saving a run lowers the run environment and thereby increases the value of each run scored. If a team wins a game by a 1-0 score, the value of a HR in that game is higher than a HR in a game won by a score of 7-3. Maybe Cameron's argument is really just a restatement of the need to use park factors in making comparisons. But there could be another issue raised by his argument which goes beyond park factors; suppose a team's pitchers are good at pitching a lot of low scoring games, does that mean the hits and walks of the batters on that team are also more valuable than they would be if the hitters were playing for the Pirates, whose pitchers give up over 5 runs per game? What if the team's pitchers are much better at home, does that mean that hitters on the team with good home batting splits are worth more to the team than if they had even splits? Obviously, park dimensions and other location factors, like wind and elevation, play a role. But sometimes park factors won't explain why batters or hitters are better or worse at home or on the road.
Think about the Astros this year. The Astros' pitching staff is much better at home than on the road--despite the fact that Minute Maid Park is completely neutral (according to Baseball Reference.com) for pitching. The Astros' pitchers have a 4.64 ERA on the road and a 3.43 ERA at home. Astros' pitchers allow an OPS+ of 94 at home and 104 on the road. Astros' pitchers allow a slugging percent of .425 on the road and .374 at home. The K/BB rate for Astros pitchers at home is 10% higher than on the road. Does this mean that the Astros' batters with strong home splits are more valuable to their team, because they are contributing more toward wins, given the pitchers' ability to lower the run context in Minute Maid Park?