How does stress factor into a pitcher’s workload?

Browsing through my RSS reader on Friday, I caught this bit by Tom Verducci of SI. From a guy with a namesake “rule” regarding pitcher usage, I couldn’t resist the title: “The problem with innings counts…” There are, of course, a number of problems with evaluating a pitcher on innings count and nothing else. That’s why the Verducci Rule is a rule of thumb: it is not intended to be strictly accurate or reliable for every situation. (From Wikipedia). Instead it’s a guideline. Surely teams use more advanced analysis to determine a pitcher’s workload.

This, of course, relates to Joba Chamberlain. He’s tossed 139.2 innings so far this year, after topping out somewhere around 120 innings a few years ago. The rule of thumb says a 30-inning increase raises a red flag, and Joba is fast approaching that number. The Yanks, for their part, are keeping Joba’s starts short now in hopes that they can keep his innings in check for the regular season.

Verducci makes an interesting comparison of Joba to two other young starters, Rick Porcello of the Tigers and Randy Wells of the Cubs. Both have about the same innings total as Joba, but there are factors which separate them. The one which concerns me most: plate appearances with runners on base. Those are considered higher stress situations. The pitcher has to worry about runners as well as the hitter, and generates less natural force by pitching from the stretch.

Chamberlain also leads the troika in overall pitches, and by a decent margin. So while he’s tossed a similar number of innings, he’s been under greater stress because of more runners on base and more pitches thrown in those innings. If we’re using innings as a measuring stick for work load, we certainly have to take these factors into consideration as well. They can help to more accurately judge how hard a pitcher works.

There are some other differences between Joba and his comps. Wells is a 26-year-old, so he’s out of Verducci’s range, which covers players 25 and under. His workload is less of a concern at that point, as his body is more physically mature. Porcello is just 20 years old and is in his second season of pro ball. Joba may lack experience, but Porcello has even less.

The comparisons are important, and I don’t think Verducci painted the whole picture here. It does show the high number of situations Joba has faced with runners on, and his high overall pitch count. But I’d like to see those juxtaposed with pitchers at Joba’s experience level, both past and present. I think that would give us a better idea of Joba’s actual work load. With access to these numbers we could whip up one of those fancy excel spreadsheets on which some fans like to play the games.

These numbers are a bit concerning. Joba will end the season with a sizable increase to his previous high in innings pitched, and far over his 100-inning total from last year. He’s throwing a good number of high-stress innings, and has a high overall pitch total. I wonder how these factors play into the Yanks overall evaluation of their struggling 23-year-old, and which others they’re using.