Francisco Liriano is coming off one of his worst outings of the season, surrendering five runs on hits through five innings against the White Sox on Wednesday night. It wouldn’t really be worth mentioning, just a blip in what has been a fantastic season, except that Liriano had gone 94 innings without surrendering a home run: from May 20th in Fenway Park until Andruw Jones smashed a 3-run homer in the second inning. Liriano has given up just three home runs all year, and his 0.18 HR/9 rate is the lowest of all qualified starters in baseball, with Josh Johnson’s 0.38 mark a close second. He’s also the first American League starter to pitch more than 140 innings and surrender fewer than 5 home runs since Ken Brett in 1976. Liriano is on pace to surrender just seven home runs this season, and for fun, here is a list of qualified starters who have surrendered seven home runs or less than 1969 (when the strikezone was decreased and the mound was lowered; it wasn’t unusual to give up fewer than 10 homers in a season before that):
Quite a list of hall-of-famers, future hall-of-famers, guys who belong in the hall of very good, and others who never really did much after that. Danny Jackson in particular seems to have gotten extremely lucky that year, surrendering six home runs despite the fact that he gave up a hit per inning (a 9.4 H/9 rate) while boasting a 1.26 K/BB ratio. This is why single-season stats aren’t indicative of anything; anyone can look good for an entire season, and sometimes a player can be lucky for an entire season. It would be a great accomplishment if Liriano manages to maintain his miniscule home run rate the rest of the season, but it doesn’t mean he’s the next Andy Pettitte.
It is unusual for a starting pitcher to surrender so few home runs over an entire season, since it takes a combination of both skill and luck to keep fly balls in the ballpark. It varies from year to year, but even the most effective ground-ball pitchers typically see about 9% of their fly balls leave the yard (this season, the league-average HR/FB% for all starters is about 9.07). In fact, most ground ball pitchers have a similar HR/FB rate as fly ball pitchers; they just don’t give up as many home runs because they don’t give up as many fly balls. For example, when Fausto Carmona was competing with teammate C.C. Sabathia for the Cy Young in 2007, he posted the highest GB/FB% in the league, at 2.97. While he didn’t surrender many home runs (just 16, for a 0.67 HR/9 rate), 11.1% of his fly balls turned into home runs. Liriano, by comparison, has a GB/FB % of 2.09 but a HR/FB% of just 2.9%. So, while Francisco Liriano has pitched well this season by both traditional and advanced metrics (3.45 ERA, 2.31 FIP, 2.99 xFIP, 3.30 K/BB), he’s also been incredibly lucky that so few of his fly balls have turned into home runs. Considering how unlucky he’s been on balls in play in general (.350 BABIP), Liriano is having one statistically odd season.