Anatomy of a player: Bronson Arroyo

Bronson Arroyo has been pitching in the majors since 2000 and has made a name for himself with his long hair and big leg kick. That is kind of unfortunate because what people sometimes miss is how good a pitcher he is.

While his ERA has not been fabulous all the time, his FIPs since 2004 have been 3.87, 4.41, 4.14, 4.51 and 4.12 this year despite an ERA above five. Every team in the league would be able to find a spot for Arroyo in the rotation, most near the front end. Because he pitches in a great park for offense on a team that hasn’t been very good recently, he is often overlooked, but Arroyo can pitch. Besides the high leg kick and the hair, Arroyo has some other unique qualities that I would like to examine using PITCHf/x.

While Arroyo throws a pretty standard set of pitches—fastball, change-up, slider and curveball—the movement he gets with these pitches is unique. Here is a look at that movement from 2008.

The first thing that jumps out at me is how much spread he has on each pitch. I’ll look more at this in a minute, but let’s start with his fastball and break things down pitch by pitch.

Arroyo’s fastball is a four-seamer that he throws around 89 mph, which is about two mph lower than league average. His average fastball has slightly below league average movement both horizontally and vertically. Probably because of this, Arroyo throws his fastball less than many pitchers, only 42 percent of the time. If you are going to throw your fastball that infrequently, you’d better have some good off-speed pitches. Arroyo has that in spades.

His change-up is a straight change, which he hides in his fastball incredibly well. His movement with the pitch is almost identical to his fastball, but thrown seven mph slower. That differential is less than many pitchers who are considered to have excellent change-ups, but it works for him because he hides the pitch in his fastball.

While his change is a good pitch for Arroyo, his slider is out of this world. He gets tremendous horizontal movement, averaging nearly 10 inches of movement compared to a ball thrown without spin. That is nearly the same movement that Barry Zito gets with his lollipop curve, only Arroyo is turning it on its side. No other pitcher who throws a four-seam fastball gets even close to that kind of movement with his slider. That kind of movement is generally reserved for the sinker/slider pitchers. To see just how crazy this pitch is, let’s look at a top view of his slider and fastball for reference.

This trajectory is generated from averaging his fastball and slider with a horizontal distance of 55 feet as the back of home plate and zero feet as near the mound. Negative depth means the ball is moving toward a right-handed batter. The tick mark represents the ball at 0.075 seconds. So Arroyo’s slider starts out looking like it is going to hit a right-handed batter and then bends to nearly the outside corner of the plate! You often hear of left-handed batters having this problem with left-handed relievers but this has to be incredibly difficult for right-handed batters to deal with.

In fact, right handers have an OPS of .665 against Arroyo in the last three years. So sit as many right-handed batters as possible against him.

The last pitch we have to look at is his curveball. Arroyo’s curve looks a lot like his slider, only he throws it about four mph slower and with a little more vertical movement on average. This actually is a triumph of my pitch classification algorithm; there is no way I would have pulled out those pitches if I were classifying them by hand because of the similar movement. You rarely see a pitcher with a curve and a slider that are so close together, but that is exactly what Arroyo has.

Why does he do it? I am guessing as another tool to keep batters off his slider. Think of it this way: A pitcher throws a straight change with almost the same movement as his fastball, but at a slower speed. Arroyo is basically doing a similar thing with his curve. It is almost like a change-up for his slider! This has to be so annoying to batters who are sitting on the slider and instead get a pitch that breaks like a slider but is slower with a little more downward motion.

So now I want to get back to the large variance Arroyo is getting with his pitches. Astute readers may already have guessed the reason for this from the top view of his fastball and slider. Arroyo changes his arm angle constantly. He generally throws his fastball from a pretty over-the-top position and drops down nearly sidearm for his slider and curve but not always. Here is a plot of his release point, zoomed in so we can see the detail.

You can see the large range Arroyo uses and generally where he throws each type, but every once in a while he will throw a fastball from the side or a curve over the top. Talk about a great way of keeping batters off balance. Try picking up the ball well when it is being released from any spot within three feet!

Additionally, as Arroyo drops his arm angle, the movement of his pitches goes from mostly vertical to mostly horizontal and pretty much anything in between because the spin axis of the ball is changing. Usually if a pitcher tries something like this his command suffers, but Arroyo’s command is excellent—he’s walked only about 2.5 batters per game the last few years (though this year it is up to 3.4). How Arroyo can have such good accuracy is completely beyond me. Here are two pictures of Arroyo’s delivery, one more over the top and one more side arm.

Bronson Arroyo’s over the top delivery. Reds vs. Astros April 23, 2008 (Icon/SMI)	Bronson Arroyo’s side arm delivery. Reds vs. Astros April 23, 2008 (Icon/SMI)

The last thing I want to mention is Arroyo’s famous leg kick. From Arroyo’s bio on his website:

Arroyo’s delivery is somewhat unique; he incorporates a leg kick in his pitching motion, extending his front leg completely straight and lifting it up to a level above his waist before delivering the ball. His kick often appears to reach head level and deceives hitters with its exaggerated motion. From the set position, his leg-kick is much less pronounced and his delivery to home plate is very quick by major league standards.

So an interesting thing to look at is how Arroyo’s stuff change when he goes into the stretch. I have plotted Arroyo’s movement for pitches thrown when a runner is on first base and no runner on second to try to ensure he is working from the stretch.

You will notice that the movement on Arroyo’s pitches is exactly the same as when he is pitching from the wind-up. In fact, even the velocity of his fastball stays almost identical from the wind-up to the stretch. The only small difference is he is throwing a few more fastballs while in the stretch, presumably to get the ball to the catcher quicker in case the runner is going. This means that his high straight leg kick is really just for show and isn’t adding anything besides deception. Measuring this deception is slightly beyond our capabilities right now, but in the not-too-distant future, with some refined metrics, we should be able to get a pretty good idea of how much that leg kick is helping.

In conclusion, Arroyo not only survives but thrives in this league with a relatively mediocre fastball by changing his arm slot and throwing excellent off-speed pitches, especially his slider. It appears his leg kick is purely for deception, as neither his movement nor his velocity is different when he goes into the stretch.

If you enjoyed this article I highly recommend you also read Derek Carty’s excellent analysis of Arroyo’s teammate, Johnny Cueto, from last week.

References & Resources
This has been long overdue but I would like to thank Cory Schwartz of MLBAM for going above and beyond his job with his help. I don’t know who Cory’s boss is, but if you happen to be reading this, Cory deserves a raise.