Here's a statistic you've probably heard a million times in the last week: Francisco Liriano has a 1.47 ERA at home and a 4.33 ERA on the road. Here's something you'll hear a lot less: why he has a much higher ERA on the road.
I can think of some reasons. Most players tend to play better at home than on the road, which is one reason it would be great if the Pirates could take two of three against the Reds this weekend. Also, PNC Park is a nice park to pitch in, particularly for a lefty, since it's hard to hit home runs to left field. But, really, that's about it. That explains a relatively small percentage of Liriano's massive home-road disparity this year. It certainly doesn't explain all of it.
So let's ask the question again: Why is Liriano's ERA so much better at home than on the road? Like, three times better? I don't know. Liriano's peripheral numbers at home and on the road are, broadly, pretty similar, and the main difference between his home and road numbers is that he has a line drive percentage of 29.4% on the road, compared to 17.3% at home. It's not a huge surprise, then, that his BABIP is 104 points higher on the road than it is at home.
Can anyone come up with a good reason why Liriano suddenly starts allowing tons of line drives on the road? I can't. He still strikes out plenty of batters on the road; he has walked a few more batters away from PNC Park, but not that many more. His xFIPs at home and on the road are virtually identical, at 3.10 (home) and 3.14 (away). It's just that he's allowed lots and lots of line drives on the road.
Which is more likely: that Liriano for some reason starts throwing batting practice just because the seats behind home plate are the wrong color, or that the very large home/road disparity has something to do with the fact that we're looking at small samples here? I'd argue that it's the latter. Home-field advantage is real, and we should expect Liriano to do worse on the road (and in his career, that's exactly what's happened). But we shouldn't expect him to be this much worse, and whether the Pirates end up playing their one-game playoff in Cincinnati or Pittsburgh certainly shouldn't impact whether Liriano starts or not, as I've heard some people suggest. (Besides, the most likely alternative would be A.J. Burnett, who has a 2.37 ERA at home this year and a 4.50 ERA on the road. That road ERA is even worse than Liriano's.)
The Reds' three best hitters -- Joey Votto, Shin-Soo Choo and Jay Bruce -- are all left-handed. We should be focusing on left-right splits, not home-road splits. Francisco Liriano eats left-handed hitters for breakfast. Lefties are hitting .130/.175/.146 against him this year. He hasn't allowed a single home run to a lefty this season. Good luck, Joey Votto. And unlike Liriano's home-road splits, where you eventually have to shrug your shoulders and admit you don't really know why they're that big, it's pretty clear why Liriano destroys lefties -- because he's left-handed, and his slider buckles the bee's knees. According to Fangraphs, only Yu Darvish has had a more effective slider than Liriano's this year.
Of course, Liriano's domination of lefties has taken place in a small sample this year, too. But which do you think is the more salient description of Liriano: that he's great at pitching to lefties, or that he's bad at pitching on the road? I think it's pretty clearly the former, and I think he's the right choice to start the one-game playoff, regardless of the ballpark.