June 28, 2013 posted by Josh Kay

Roberto Hernandez’s Home Run Problem

Roberto Hernandez’s Home Run Problem
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The artist formerly known as Fausto Carmona is teasing the sabermetric community thanks to his performance to date with the Rays. The thirty-two year old Roberto Hernandez (his real name it turns out), has posted an excellent 3.45 xFIP (an expected ERA metric centering around a 10.5% HR/FB standardization) that belies his current 4.98 ERA he has recorded through 15 starts so far in 2013. Unfortunately for Hernandez, the resulting gap between his ERA and xFIP is due to his current 21.1 percent home run per fly ball rate, and also a 1.49 home runs per nine innings rate.

Through his 90 innings thus far, Hernandez has posted a 19.5 percent strikeout rate and a 5.4 percent walk rate. There is no doubt those are excellent results, the problem is Hernandez’s 23.6 percent line drive rate. His career line drive rate is 16.2 percent. What’s more concerning is that those line drives are coming at the expense of his usually high ground ball rate (57.9 percent for his career), as that number comes in at 51.4 percent in 2013.

The Rays have tapped into a Hernandez, or even a Carmona, that Major League Baseball has never seen in terms of a high strikeout rate and a minimized walk rate. Hernandez’s only full professional season with a walk rate lower than seven percent was during his 2007 career year.

During that season, (the at the time Carmona) Hernandez went 19-8 with a 3.06 ERA, a career best 64.3 percent ground-ball rate, a 0.67 home run per nine innings rate, a 15.6 percent strikeout rate and a 6.9 percent walk rate.  Hernandez would never sniff those numbers again until this season with the Rays.

Now, before deciding whether or not Hernandez has returned to peak form (in terms of peripherals), we must decide whether we can trust his current strikeout rate to be an “improved pitch”, a change of approach orchestrated by the excellent Rays pitching coaches, or an unsustainable peak mechanics hot streak.

It turns out there is some good news; this strikeout rate is to be trusted. Hernandez always had shown a potent changeup in terms of whiff/swing rates. The problem has been the pitch’s lack of usage. The following data (and a large amount of other data seen in this piece) is retrieved from the excellent Pitch F/X site

Year Usage Rate Whiff/Swing Rate* BAA/SLG/ISO BABIP
2007 14.79% 30.43% .194/.269/.075 .255
2008 10.70% 31.53% .260/.300/.040 .342
2009 20.10% 31.15% .211/.346/.135 .255
2010 13.93% 31.95% .228/.293/.065 .289
2011 18.99% 28.34% .228/.329/.101 .272
2013 29.67% 29.73% .211/.316/.105 .259


*Whiff/Swing rate refers mathematically to the percentage of times a batter misses when he swings. Ex: if Hernandez induces 100 swings on his change-up over a given span of time, batters miss on 30 of those swings. His career whiff/swing rate on the changeup is 29.99 percent.

So given the increased usage of his excellent swing and miss change-up, it’s extremely logical that his strikeout rate has climbed to a career high rate. That means all Hernandez has to do is keep pitching the way he has been and wait for his home run per fly ball to regress down to his 12.1 percent career mark and his ERA will end up around 3.60 or so. Seems simple enough right?

Not so fast, that’s lazy analysis.

Hernandez’s problems run deeper than home runs. Home runs are a bi-product of his chronic problems vs. left handed batters. Here are his career left and right handed batter splits for his career. (Data courtesy of Fan Graphs)

Split K% BB% Infield Fly Ball % LD% wOBA
Vs. L 11.6% 9.2% 5.0% 18.1% .353
Vs. R 17.3% 7.8% 12.6% 13.6% .309


Not only has Hernandez been better in terms of strikeouts and walks, he clearly induces much weaker contact from right handed batters compared to left handed batters.

In 2013, his peripherals against both have been much better, but his peripherals against right handed batters have been particularly absurd.

Split K% BB% Infield Fly Ball% LD% wOBA HR/9 HR/FB%
Vs. L 17.4% 7.8% 2.1% 24.8% .366 1.98 23.4%
Vs. R 21.3% 1.9% 25.0% 21.8% .290 0.89 16.9%


The major takeaways from this set of data is his incredible K:BB ratio against lefties. Notice it’s the same as his ratio against righties throughout his entire career. His line drive rate hasn’t suffered the same fate, as it’s been much worse than years past. Of course, the real issue when line drive rate climbs is an issue of velocity and the pitcher making too many mistakes. Hernandez’s combined velocity between his fastball and sinker started at 94.96 miles per hour during his 2007 career year. Since 2007, it has dropped every season all the way down to 92.20 miles per hour where it is now.

Somewhat unsurprisingly his line drive percentage has increased in direct correlation with his velocity decreases, except in 2010 where his line drive rate dipped back down to 13.6 percent before spring-boarding back up to 18.6 percent in 2011.

Hernandez’s biggest problem has been home runs against lefties. Once again, unsurprisingly, the pitch that has plagued him has been the sinker. Hernandez has abandoned the fastball this year, throwing it six percent of the time (a good decision since it was always his worst pitch).

Let’s take a look at Hernandez’s results against left handers.

Fastball 7% .600/.1000/400 .750
Sinker 46% .333/.618/.284 .351
Changeup 15% .197/.268/.070 .228
Slider 32% .222/.482/.259 .211


The changeup reigns supreme; and once again we see the problems with the sinker and fastball. But that’s enough data, the question on fantasy owners minds at this point is “Is Hernandez usable, can we trust him, and will his home run per fly ball decrease, specifically against lefties”.

The answer lies with pitch selection. Hernandez has used unbelievably stupid pitch selection with two strikes against left handers. Lefties hit .262/.643 (batting average/slugging) with a .353 batting average on balls in play against Hernandez’s sinker with two strikes. This opposed to a .200/.314 against his changeup with two strikes (.286 BABIP).  This graphic of his two strike sinker locations proves it all (sorry I lied about no more data).

plot_profile hernandez 2 strike sinkers

Anyone wonder why those pitchers are getting hammered? They are right in the happy zone and they come with two strikes. That’s poor decision making.

Our recommendation is to monitor Hernandez in shallow leagues and to add him reserve him in deeper mixed leagues (if already owned in such leagues keep him on your watch list). Start him freely against right handed heavy lineups such as the White Sox and Brewers, as well as teams with lefties that aren’t exactly power hitters. Keep track of Hernandez’s pitch usage during his starts. If he begins to use the change-up more often and the sinker less often, pounce. Until then, he’s not a candidate for “positive regression to the mean”.


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