The discussion surrounding home runs per fly ball has been interesting to say the least. It has spawned some deep discussion and a bunch of new research into determining if it is a skill, including some research done by yours truly that you can find here.
Today, there is a new advancement on the subject. Jesse Wolfersberger of Fangraphs first created a regression model that gave the expected home run rate and has now used that to try to estimate the effect of a pitching coach in preventing home runs.
He looked at the data from 2002 to 2010 of the four pitching coaches who have been with the same teams and found some very interesting results with regards to Giants' pitching coach Dave Righetti.
For the most part, the model splits each coach’s qualified pitchers in half between those who outperformed their expected HR/FB rate and those who underperformed their projection. Righetti is the only exception. Of the 44 qualifying pitcher-years in Righetti’s reign with the Giants, 38 had a lower HR/FB rate than the model predicted. Considering none of these other coaches had even 60-percent of their pitchers fall on one side or the other, Righetti’s 86-percent rate of starters outperforming their expected HR/FB is simply stunning.I think it's pretty safe to say with a nine year sample, this is beyond simple luck and something interesting is happening to produce consistently low home run rates.
The results stay the same when you look at total innings of the Giants pitchers under Righetti:
Righetti is the only pitching coach who seems to have any significant effect on HR/FB rate, and it’s decidedly negative. His starters have a HR/FB almost two standard deviations away from the model’s expectations, while none of the other coaches are over one standard deviation in either direction. Also note that this looks at more than 8,700 innings under each coach’s tutelage. To outperform the model’s expected rate, which predicts the Giants to have a below-average HR/FB already, seems beyond the bounds of luck.Check out the full article because there is too much good stuff to excerpt and there are some nice tables that summarize things.
The Giants pitchers have suppressed on average 25 home runs a season. When that is converted into runs, it translates into about 35.5 runs prevented a year, or a little over three wins. With the marginal cost of a win in the $4-5 million range, Righetti has given the Giants a value in the range of $100 million on his teachings on home run prevention.
Someone give that man a raise.
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