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What Pitchers Improved the Most and Declined the Most, 2005-6

Last week I looked at the hitters. This week it is the pitchers. I used two metrics: RSAA (Runs saved against average) from the Lee Sinins Complete Baseball Encyclopedia and a very simple defense or fielding independent version of ERA. The pitchers I looked at were generally starters only, since my IP minimum was 100 for both seasons.

Let's start with RSAA. "It's the amount of runs that a pitcher saved vs. what an average pitcher would have allowed." It can be negative and it is adjusted for park effects. The table below shows the pitchers who made the biggest improvement in RSAA per 9 IP.

Here positive is good. It means you are saving more runs than the average pitcher. Now for the worst

One problem here is that runs allowed is affected by the fielders, too. So I ran a regression in which ERA was the dependent variable and HRs allowed, walk (including HBP), and strikeouts, all per 9 IP. Here is the equation

ERA = 2.89 + 1.41*HR + .37*BB  - .20*K

The table below shows the biggest improvements. Here negative is good. It means the guy lowered his fielding independent ERA

Now for the biggest decliners.