Edward Mujica, right-handed pitcher for the San Diego Padres, is a pretty good middle reliever. Check out his numbers since coming to the Padres:

Year Innings ERA K/9 BB/9 FIP xFIP tRA
2009 93.7 3.94 7.3 1.8 4.03 3.93 3.61
2010 31 3.19 9.3 1.2 4.79 3.10 3.94

The strikeouts and walks look good. There is one thing I purposely left out, however, and that is home runs allowed. Mujica has given up 22 home runs in 124.7 innings as a San Diego reliever. That is a 1.6 HR/9 rate. He will have trouble staying in the majors if he continues to allow home runs at this pace. Of course, perhaps he has just been unlucky or in a slump.

We now have a variety of tools at our disposal to investigate Mujica’s home run troubles. First, let’s look at his ball-in-play rates (note that 2006-2008 with Cleveland is a pretty small sample, about 70 innings total):

Year Line Drive Ground Ball Fly Ball IFFB HR/FB
2006 18.5% 26.2% 55.4% 19.4% 2.8%
2007 16% 26% 58% 17.2% 10.3%
2008 23.4% 30.5% 46.1% 10.2% 8.5%
2009 17.2% 39% 43.8% 7.9% 11%
2010 12.3% 40.7% 46.9% 0% 21.1%
Career 17.9% 35% 47.1% 9.7% 10.7%

IFFB: Infield Fly Balls
HR/FB: Home runs per fly ball

According to FanGraphs, the approximate 2010 averages are:

LD: 18.5%
GB: 44.6%
FB: 37.2%
IFFB: 9.5%
HR/FB: 9.3%

What we have in Mujica, then, is a pretty extreme fly ball pitcher. He has a career fly ball rate of about 47%, while the league average is 37%. He is pretty average on line drive%, IFFB%, and a bit over the league average on HR/FB%.  One interesting thing to note is that his infield fly ball percentage is at zero so far this season. So, apparently, every fly ball he has allowed has gone into the outfield. That is probably not helping his HR/FB rate.

Anyway, the sabermetric literature suggests that home runs are essentially a function of fly ball percentage. In other words, HR/FB should regress heavily toward the league average. Let’s take a look at Mujica’s actual home run rate and his home run rate after adjusting his HR/FB to the league average 9.3%.

Year HR/9 ADJ. HR/9
2006 .49 1.6
2007 2.48 1.9
2008 1.16 1.3
2009 1.35 1.1
2010 2.32 1
Career 1.43 1.24

Since 2009, if Mujica had allowed a league average HR/FB rate of 9.3%, his overall home run rate would be about average. While Mujica is a fly ball pitcher, his strikeout and walk rates are good enough that his propensity to allow fly balls should not be an issue, *if* he puts up league average HR/FB rates. Over these past two seasons, however, he has actually given up 22 homers on 135 fly balls, good for a 16.3 HR/FB%.16.3% is a different story.

Hit Tracker gives us another interesting tool to analyze Mujica’s home run struggles. Before looking at the data, the theory would go that, since Mujica has probably been “unlucky” so far in his Padres career (especially 2010), a lot of his home runs allowed should be unlucky home runs, homers that just barely got out.

Here are some definitions from Hit Tracker:

Std Distance (Standard Distance) – The estimated distance in feet the home run would have traveled if it flew uninterrupted all the way down to field level, and if the home run had been hit with no wind, in 70 degree air at sea level. Standard distance factors out the influence of wind, temperature and altitude, and is thus the best way of comparing home runs hit under a variety of different conditions.
“Just Enough” home run – Means the ball cleared the fence by less than 10 vertical feet, OR that it landed less than one fence height past the fence. These are the ones that barely made it over the fence.
“No Doubt” home run – Means the ball cleared the fence by at least 20 vertical feet AND landed at least 50 feet past the fence. These are the really deep blasts.
“Plenty” home run – Everything else, except for the 2 above Homerun types
Lucky Homer – A home run that would not have cleared the fence if it has been struck on a 70-degree, calm day.

Here are Mujica’s eight home runs allowed this season:

Hitter Location Type Std. Distance
Davis NYM No Doubt 446
Davis SD Just Enough 408
Blake LA Just Enough 384
Lee HOU Plenty 406
Pence HOU Just Enough 426
Sandoval SD Plenty 436
Reynolds SD Plenty 381
Upton ARZ No Doubt 454

Mujica’s average Standard Distance is 418 feet (NL average: 395). The home run to Blake in Dodger Stadium is the only “lucky” home run Mujica has given up:

mujica HR

Here are the landing spots on all of Mujica’s home runs allowed this season:


He has given up some absolute bombs, some normal home runs, and a couple of borderline ones. It is tough to make any real conclusions based on this data because of the sample size. For a little additional context, last year Mujica’s Standard Distance on his 14 home runs allowed was 387 feet. He gave up four in Petco Park and 10 on the road. Six were classified as “plenty” and eight as “just enough.”

If anything, I think we can say that this season Mujica’s homers allowed have not been of a particular unlucky nature. For the most part, they have been hit hard. Of course, that is not to say that he hasn’t been unlucky. After all, it is still a small sample and there are a lot of variables that go into a home run: bad pitch selection, bad execution, the hitter’s swing, etc. Perhaps Mujica has thrown good pitches that hitters have handled, or maybe he’s just thrown a few bad pitches that have been hammered.

We have yet another tool at our disposal: PITCHf/x. I am just going to look at 2010 data, identify Mujica’s pitch types, usage, and then specifically look into his home run pitches.

According to PITCHf/x, here is what Mujica throws:

Pitch Type 4Seamer 2Seamer Change Curve Slider Cutter
Velocity 92 89.9 86.9 81.4 82.8 89.7
Usage 54.8% 4.5% 27.6% 5.1% 6.9% 1.1%

Here’s the pitch movement graph (x-axis: horizontal movement, y-axis: vertical movement, view from catcher’s perspective):

mujica pitch movement

Mujica throws a split-finger fastball quite often (20% of the time for his career, according to BIS) that PITCHf/x apparently does not pick up on. It appears to me that the changeups classified by PITCHf/x are actually splitters. Here’s a good look at Mujica’s pitches from a bird’s eye view:

mujica flight path

If you look closely enough, you can see the four and two seam fastball, along with the splitter (classified as a change), move in on a right-handed hitter. The cutter, slider, and curve all break in the opposite direction.

Anyway, the last thing I wanted to look at is the location and pitch type on Mujica’s home runs allowed this season:

Mujica, homers allowed

Four homers on four-seamers, three on splitters (I reclassified the changes as splitters), and one on a slider. All located in prime home run territory, up and out over the middle of the plate.

If we’ve learned anything from this, it’s that we can analyze a player’s performance in a lot of different ways and, in the end, still be left with more questions than answers. Mujica is a flyball pitcher who is going to give up his share of home runs. However, if small sample size and regression mean anything to us, he won’t continue to give them up at this rate. At the same time, nobody wants to be testing any mathematical theories in the middle of a pennant race.