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March 3, 2004
Baseball Prospectus Basics
How We Measure Pitcher UsageSo to understand the methods we use to analyze pitcher usage, it's important to appreciate that while every team in baseball today employs essentially the same usage pattern--starting pitchers work in a five-man rotation, with four or five days of rest between starts, and never relieving in between--that usage pattern is far from the norm historically.
So if starting pitchers have been used in many different ways over the years, and there's no hard evidence that any one usage pattern was more likely to keep pitchers healthy, how do we determine whether a pitcher is being used in a manner that's likely to get him hurt?
One thing we have learned is that for starting pitchers, how many days off they get between starts does not seem to correlate with injury risk. This series of articles carefully looks at the track record of pitchers working in a four-man rotation vs. pitchers in a five-man rotation, and finds that pitchers who worked in a four-man rotation stayed just as healthy as pitchers working every fifth day. It also showed that a pitcher working on three days of rest is no less effective than when he works on four days of rest, and in fact that he might have better command on less rest.
What seems to matter isn't how often a starter pitches, but how much he pitches when he does take the mound. About five years ago, we unveiled a system known as Pitcher Abuse Points (PAP for short) that attempted to measure just how much is too much. The system is based on the following principles:
The original version of PAP operated under the assumption that fatigue set in at 100 pitches, and after 100 pitches a starter was awarded Abuse Points for each additional pitch. The number of points he received per pitch slowly increased as he threw more pitches.
Two years later, Keith Woolner performed the definitive study that examined the relationship between high pitch counts and injury risk. First, Woolner looked at whether there was a relationship between high pitch counts and decreased effectiveness over the pitchers next few starts. What he found was that, while the relationship was there, the formula for PAP needed to be changed--that until that point, the system did not penalize pitchers enough for really high pitch counts (120 and up) compared to a 105 or 110-pitch outing.
Then using the new, refined formula for PAP, Woolner showed that there was, indeed, a link between high PAP scores and future injury risk.
The way PAP scores are calculated is quite simple. Simply take the number of pitches thrown in any given start, and subtract by 100. (If the pitcher threw fewer than 100 pitches, he automatically receives zero PAP for that outing.) Then the resultant number is cubed to arrive at the PAP score for that start:
100 pitches - 100 = 0^3 = 0 PAP 105 pitches - 100 = 5^3 = 125 PAP 115 pitches - 100 = 15^3 = 3375 PAP 130 pitches - 100 = 30^3 = 27000 PAPAs you can see, by this method a 130-pitch outing is eight times more damaging than a 115-pitch start, and 216 times worse than throwing 105 pitches.
There's one other factor that needs to be considered when evaluating whether a starting pitcher is throwing too many pitches. As first explored by Craig Wright in his landmark book, The Diamond Appraised, starting pitchers under the age of 25 appear to be particularly sensitive to how many innings they are allowed to throw. Some of the most talented young pitchers of the last forty years--from Gary Nolan and Don Gullett in the 1970s, to Dwight Gooden in the 1980s, to the Mets' "young-guns" trio of Bill Pulsipher, Paul Wilson, and Jason Isringhausen in the 1990s--went on to suffer career-threatening injuries that prevented them from ever reaching their full potential. Conversely, two of the most durable starters of our generation, Nolan Ryan and Randy Johnson, weren't even full-time starters in the majors until they turned 25.
Indeed, when 21-year-old Kerry Wood blew out his elbow, the spring after one of the most exhilarating seasons ever by a rookie pitcher, it proved to be the spark needed to convince major-league organizations that lowering the pitch counts of their starting pitchers might prevent a significant number of injuries--and save them millions of dollars in the process.
So to recap, here's everything we know about the usage of starting pitchers:
The ideal usage pattern--something I think we'll see some teams try to emulate over the next decade--would probably look something like this:
Individual starting pitchers throw fewer innings, and therefore have less overall value, today than at any point in baseball history. But it doesn't have to be that way. By following these guidelines, teams should be able to safely get 280-290 innings out of their #1 starter, instead of the 220-230 innings we see today.