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Talking Sabermetrics: Two Pitching Topics

HOUSTON - Bud Norris throws a lot of sliders.  (Photo by Bob Levey/Getty Images)
HOUSTON - Bud Norris throws a lot of sliders. (Photo by Bob Levey/Getty Images)
Getty Images

Both sabermetric topics today are related to Astros' pitchers. The first question is whether the types of secondary pitches thrown by pitchers affects the liklihood of future injury. Baseball people have argued about this for some time. A fangraphs article attempts to shed some light on the subject with data. And I will look at the implications for Astros' pitchers this year. The second question I will examine is which Astros' relief pitchers are under performing the SIERA statistic by the biggest margin.


Over the years, a lot of baseball people believed that sliders add stress to the arm and, therefore, increase injury risk. Other breaking pitches, like the curveball, have also been considered an injury risk relative to the fastball. However, a sports medicine book recently challenged the presumption that sliders and curveballs are physiologically more stressful on the arm.

For this question, some sabermetric research on pitching data may help. A short Fangraphs article by Jeff Zimmerman a few months ago concluded that pitchers with extreme slider or curveball usage were more likely to incur Disabled List time. (Bud Norris and Wandy Rodriguez were included in the slider and curveball group, respectively.) Fangraphs' Bill Petti recently wrote about a study he performed on pitchers' secondary pitches and the impact on the pitchers' attrition rate (measured by a reduction in innings pitched) in the next year. Attrition rate is assumed to be related, at least in part, to injuries. Although his findings are not conclusive, this article arrives at some interesting relationships.

You can read Petti's article to get the full discussion. But here are the main findings as I see them: (1) The type of secondary pitch thrown by a pitcher, in itself, has minimal impact on attrition rate; (2) The extent that a pitcher relies on a single secondary pitch increases the risk of significant innings attrition; (3) Extreme usage of the slider and curveball increases the pitcher's attrition rate, but higher usage of the change up as the main secondary pitch decreases the pitcher's attrition rate.

So what does this mean for Astros pitchers? For that question, let's look at Astros' pitchers who have used the curveball or slider more than 35% this year. That threshold seems like the point at which usage is extreme enough to have a negative effect on the pitcher's risk.

Bud Norris, 35.7%, slider

This isn't a real surprise. We have had occasional discussion at TCB about Norris' injury risks. Norris has been among the heaviest users of the slider in the major leagues throughout his career. In fact, his usage of the slider is slightly below his percentage reliance on the slider in the past. Petti's article indicates that the trend for sliders is more erratic when the pitchers are separated into starters and relievers, with starters perhaps less affected by heavily relying upon sliders. Whether this provides Bud a safe haven from injury risk associated with his slider usage is anybody's guess.

Brandon Lyon 48.3%, cutter

This is a very high percentage usage of the cutter by Lyon (actually the cutter is the primary pitch, and the fastball is the secondary pitch). But I don't think it necessarily means much for Lyon's injury risk. First, this is the first time that Lyon has used the cutter that much, so it may be a sample size issue. Second, cutters aren't listed among the secondary pitches in Petti's study. Cutters could be considered a cross between a fastball and a breaking pitch, but still they are usually considered a form of fastball.

Xavier Cedeno, 44.3%, curveball

This is a small sample for Cedeno, but it probably correctly reflects that Cedeno is an extreme curveball thrower. I don't know if X-man will stick with the big league club long enough for us to find out if it is an injury factor.

Wesley Wright 39.5%, slider

This heavy slider usage by Wright is something new---he has more modest reliance on sliders in past years. This is such a sharp increase that it must reflect a change in his pitching strategy.

Brett Myers, 36.1% curveball

This is the first time that Myers has used the curveball so intensively. He is far below the 35% threshold in previous years. However, as a closer Myers has gravitated to using the curveball as his strike out pitch, and lessened the use of his fastball and change up. He has also increased the usage of his slider in the closer role. Myers has undergone arm surgery during his Phillies' years, and it remains to be seen if moving the closer role has increased his injury risk.

Notice that I didn't show Wandy Rodriguez, who has been listed in previous articles as an extreme curveball pitcher. Wandy's curveballs have been used at a 31% clip this year and fell below the 35% threshold. But he has exceeded 35% in each of the three prior years. Despite the heavy usage in the past, Wandy has been fairly healthy during that period.

One notion to come out this work is that a change up pitch is a good thing. It appears to be less problematic from an arm injury standpoint. Furthermore, other analyses suggests that greater or lessor reliance on change up pitches is associated with over- or under- performance, respectively, of pitchers' peripherals. It certainly wouldn't hurt for the Astros to encourage Bud Norris to use his change up more.

The SIERA topic is after the jump.


SIERA stands for "skill interactive ERA," and is one of the advanced statistics that attempts to identify a pitcher's true skill during a performance period. SIERA is more complicated than similar stats such as x-FIP. But it is also the more predictive ERA-type statistic; that is, a SIERA stat over a season is more likely to predict future ERA than ERA, x-FIP, or FIP.

A recent fangraphs article listed J.A. Happ in the top 10 of SIERA under-performance by MLB starting pitchers. This could indicate that Happ's performance will improve in the future. Of course, SIERA at this stage of the season is subject to sample size caveats, just like any other statistic. Thus, the predictive characteristic may not be as reliable as a full season of SIERA. But it at least gives some hope that Happ's performance will improve over this season.

This led me to ask, "which Astros' relievers are the most substantial under-performers of SIERA?" I limit this question to relievers who have pitched in the bullpen most of the season (e.g., excluding Brian Bogusevic's one appearance). Fernando Rodriguez and Rhiner Cruz are the big under performers.


F. Rodriguez

6.23, 4.93, 4.24, 1.99 diff.

Rhiner Cruz

7.33, 5.74, 4.10, 3.23 diff.

Cruz has an immense 3+ run under performance. Rhiner Cruz has an ERA which might spell DFA for other pitchers. Yet SIERA says Cruz has pitched like an average major league pitcher. Cruz's biggest problem is a 16.7% HR/flyball rate----a statistic which is likely to normalize in the future. Cruz's .342 BABIP probably also will regress in the future. Although Cruz has a high walk rate (4.24 per 9), it isn't overwhelmingly bad, and is less than his recent minor league walk rates. Don't give up on Rhiner Cruz.

Fernando Rodriguez has a 2 run under performance. And his problems are more of a mystery. F-Rod's peripherals this year are not that much different from his perpherals last year, when he posted a 3.96 ERA. His K rate is still high, only somewhat below last year. His walk rate is the same as last year. His BABIP is better than last year. His HR/fly rate is only marginally higher than last year. His velocity is a notch above last year. So what gives? I would suggest that his fangraph clutch statistic holds the answer. He was +1.24 last year, but his clutch score is -0.28 this year. This is reflected in his extremely low LOB%, 56.9%, compared to 79.4% last year. To a large extent it appears that F-Rod has suffered from some bad timing on the situations and sequences when he allowed hits. F-Rod probably was somewhat lucky last year, and he is unlucky this year.