Daily Graphing – Bronson Arroyo

The Red Sox and Bronson Arroyo have agreed to a 3 three 12 million dollar contract. After Arroyo started off the year great going 4-1 with a 3.18 ERA in 9 starts, everything seemed to fall apart. Over his next 23 starts he was 10-9 with an ERA over 5. Let’s see if we can figure out what happened to Arroyo and if there’s a chance he’ll rebound in 2006.


Starting off with his strikeouts per 9 innings (K/9), it looked like he was finding his groove around mid-May, but took a serious nose dive shortly after. In 2004 he displayed a very solid K/9 of 7.1, but in 2005 he could only manage a poor K/9 of 4.3. What exactly happened here?


If you break his 2005 season down by pitch type, you’ll see that he started off the season throwing his changeup pretty much never, to throwing it nearly as much as his curveball and slider. Funny thing is, his changeups started to ramp up right around the same time his K/9 fell off a cliff. Coincidence? Probably not.

Furthermore, his changeup, with the exception of his fastball (which he throws a lot), was his most hittable pitch. When he started throwing more changeups, he also ended up throwing less sliders and curveballs, his two least hittable pitches.


It seems as though a lot of Arroyo‘s problem could be a pitch selection issue. His walks per 9 innings (BB/9) look pretty good too, so if he can manage to work on his changeup and get his strikeouts back to where they were in 2004 there’s not a bad chance he’ll be a pretty decent pitcher.

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David Appelman is the creator of FanGraphs.

3 Responses to “Daily Graphing – Bronson Arroyo”

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  1. Mike says:

    Just curious: How did you determine that his fastball and changeup where his most hittable pitch? I’m just wondering, although I do agree with you (I’m a Red Sox fan and watched enough of Arroyo). Also, he has lot’s of troubles with lefties…

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  2. David says:
    FanGraphs Supporting Member

    Well… I basically just took the percentage of hits off of each pitch type. Sort of like a batting average by pitch type, but instead of at bats, you use pitch totals. I’m sure there’s some serious flaws with this approach, but figured it was ok to use as a quick barometer.

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  3. Ken Z. says:

    Your analysis is very interesting! I would suggest that you do this same analysis broken out by left vs. right hitters. It is my observation (no numbers to back it up) that Arroyo had a lot more problems against lefties particularly with his fastball and change. I also think he faced a more lefties as the season progressed as opposing managers began to load lefties in their lineups against him. It would be interesting to see if your numbers back this up! It is my opinion that Arroyo will be a better pitcher once he finds a pitch to consistently get lefties out.

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