Originally posted on Fangraphs  |  Last updated 12/12/13
I remember the way things used to be. Used to be, writing about baseball analysis was pretty easy. Inflated or deflated BABIP over here. High groundball rate over there. This guy has a big difference between his ERA and his xFIP. That guy is miscast as a role player. That’s not the way things are anymore. Many of the principles were fine, and you still see a lot of the same ideas, but over time things have grown more complex, more nuanced. We’re moving beyond pointing out weird things, and we’re moving toward trying to explain weird things. It’s all in the name of identifying what is and isn’t sustainable. All of us want to be fortune tellers. The Phillies signed Roberto Hernandez today, as a starting pitcher. He’s going to get a base salary around $4.5 million, and with incentives he can top out around $6 million. If writing were the same as it was a few years ago, I could just write a few paragraphs about how Hernandez put up a 4.89 ERA and a 3.60 xFIP. On that basis alone, hey, look, bargain! But because of what writing and research have become, now you also get that intro paragraph. What’s known is that, in his return to the majors, Hernandez put up some neat peripherals in Tampa Bay. What’s also known is that he allowed too many runs, because he allowed too many home runs. Just about the entire story here is trying to figure out whether or not Hernandez is severely homer-prone. And, I don’t know. I’ll just put that out there now. I don’t know what his dinger rate is going to look like in 2014. But, for the record, Tim Lincecum is coming off a 124 ERA- and a 94 xFIP-, and he signed for two years and $35 million. Dan Haren is coming off a 125 ERA- and a 97 xFIP-, and he signed for one year and $10 million. Hernandez, as a starter, is coming off a 131 ERA- and an 89 xFIP-, and he signed for one year and no more than $6 million. The deal looks at least reasonable, and because it’s a one-year commitment it’s a virtually harmless roll of the dice. Something of a sabermetric roll of the dice, being attempted by the Phillies. Ruben Amaro was just talking about pitcher wins the other day. He signed a guy with a miserable ERA who also tied for 27th in baseball among starters in park-adjusted xFIP. Amaro didn’t sign Hernandez because of his xFIP, but it’s funny when certain organizations end up with surprising types of players. Here’s something to know about Hernandez. Since 2002 — as far back as the data goes — 111 starters have thrown at least 1,000 innings. Hernandez has put up an FIP- ten points higher than his xFIP-, which is the second-biggest positive gap in the pool, below only Brett Myers. One of his selling points is that he can keep the ball on the ground, but because of the homers, Hernandez’s “effective” grounder rate is quite a bit lower. It seems to be Hernandez is unusually homer-prone, and last year was a major flare-up. Again, since 2002, there have been 1,580 individual starting-pitcher seasons of at least 100 innings. Hernandez’s 2013 owns the second-highest rate of homers per fly ball, above 21%. Basically, twice the league average. Mark Trumbo just put up a rate of about 21%. The question is, all right, so what does that mean going forward? We can look at the four worst rates from the season before. Ervin Santana regressed to something much closer to average. Tommy Hunter regressed to the average, but as a reliever. Jason Marquis kept allowing a ton of homers. Henderson Alvarez rebounded to allow the lowest rate of homers per fly ball in all of baseball. So, there’s your answer. Hernandez, this coming season, will not regress at all, or he’ll move to the complete opposite extreme, or he’ll regress to the average, or he’ll regress to the average upon changing jobs. That covers literally every base. It feels like we’ve learned a lot, but really, we haven’t learned anything. Not as far as next season is concerned. The safest assumption is that Hernandez will allow dingers, but fewer of them. He allowed 24 last season, throwing about 2,400 pitches. In other words, 1% of Hernandez’s pitches wound up as a dinger, and you can see why this is a stat with so much volatility. We’re talking about roughly one pitch per game, and even good pitchers are frequently making mistakes in terms of location. The average mistake rate is way higher than 1%, and when there’s a mistake the opposing hitter still has to do what he can do to cash in. Sometimes the pitches get punished; sometimes they get swung through or popped up. Some missed timing here, some fortuitous swings or wind gusts there, and Hernandez can look a lot better. It’s clear that xFIP leaves a lot out. It’s clear that xFIP is still extremely useful, and worth keeping in mind. Better to have a guy coming off a high ERA and a low xFIP than a guy coming off a low ERA and a high xFIP. For 2014 I’d rather have Roberto Hernandez than Hector Santiago. It’ll be interesting to see if Hernandez holds on to some changes with the Phillies. The Rays had him throw a low more changeups to same-handed hitters, and a lot more sliders to opposite-handed hitters, both of which defy convention. Against righties, Hernandez posted his lowest career xFIP. Against lefties, Hernandez blew away his previous career-high strikeout rate. Lefties also torched Hernandez for 17 of his 24 homers allowed, so that could be a real concern, but as we’ve discussed, we don’t know how much of one. We just don’t. Probably can’t, at least not from here. So the Phillies will take the chance, for a year and a little money. They’ll take the chance any sabermetric writer would’ve recommended a few years ago. Absolutely, it could work out real well. Absolutely, Hernandez could keep allowing homers, because he has a problem we can’t quite put our fingers on. For a team in the Phillies’ position, better to take a cheap chance than a more expensive one. Maybe Hernandez won’t be good, but then the Phillies probably won’t be good, either. As free agents go, the right thing to target is affordable volatility.
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