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— Where BTF's Members Investigate the Grand Old Game
Tuesday, October 01, 2002
Runs Allowed Average: A Better Way to Figure ERA
Eric breathes new life into the old standby.
Earned Run Average is regarded as the best mainstream stat for measuring a pitcher?s effectiveness. I generally agree, but as I see it, there are still two fundamental problems with ERA. One, it doesn?t account for unearned runs and two, it doesn?t account for inherited runners that score thanks to bad relief pitching. The statistic described in this article, Runs Allowed Average (RAA), is an attempt to correct those flaws.
Unearned runs are still runs. They hurt the team as much as earned ones, and pitchers should be held at least partially responsible for them. Very few runs are scored due to bad defense alone. If a run scores on a hit and an error, neither the hit nor the error alone caused the run, but the combination of the two. Besides, earned and unearned runs are based on errors, which are not a particularly good measure of defense anyway. With ERA, a run scored when Nomar Garciaparra bobbles a grounder is the fielder?s fault, but a run scored on a ball that rolls past the slothlike Mo Vaughn is the pitcher?s fault. In addition, when a pitcher gets blasted during an inning in which an error happens to be made, as Pedro Martinez was on May 7, ERA lets him off scot-free. In computing RAA, then, I decided to count an unearned run as 50 percent of an earned run. This is admittedly an arbitrary figure, but it is fair, I believe, to the pitchers who genuinely have poor defensive teams behind them, and is also fair to those pitchers who help their teams by giving up few unearned runs, and who are able to bear down when an error is made behind them.
The other major problem with ERA is that it?s polluted with runs that score when relievers allow inherited runners to cross the plate. A common argument regarding the MVP award is that players on bad teams shouldn?t be penalized for having bad teammates; likewise, neither should starting pitchers be penalized for having bad relievers. The pitcher who put the man on base and the pitcher who allowed him to score should each bear some responsibility for the run, but how much? Fortunately, we have play-by-play data for recent seasons, which tells us: a) how many of these runs a starting pitcher has been charged with, and b) which base the runner was on when the pitcher left the game. I decided to go with a simple formula, which is that each base counts for a quarter of a run. If a pitcher leaves a runner on first who later scores, 75 percent of that run gets charged to the reliever, 25 percent to the starter. If a runner scores from third, 25 percent of that is charged to the reliever, 75 percent to the starter. For a runner left on second base it?s 50-50. This system is admittedly flawed in that it doesn?t take into account the number of outs when the pitching change was made, but it is much better than simply charging the run to the pitcher who put the man on base.
Below are the 2002 RAAs for nine selected pitchers: those with the top three ERAs in the AL and the top five in the NL, plus Curt Schilling. I would have included more pitchers, but I?m not smart enough to figure out how to make my computer do all the work, so I figured these out by hand, game by game. I didn?t include relievers, although I do think RAA would be a far more accurate indicator of a relief pitcher?s value than ERA.
As you can see, the end product of RAA is roughly equivalent with ERA. The nine pitchers collectively had an ERA of 2.76 and a RAA of 2.80. Most of the differences between the two stats are minor, but several are revealing. First, this year?s two ERA champions, Pedro Martínez and Randy Johnson, both have deceptively low ERAs because they allowed large amounts of unearned runs. Johnson, of course, is still easily the best pitcher in the National League. In the American League, however, it becomes apparent that the large ERA difference between Martinez and Derek Lowe is mostly an illusion. RAA is also useful in comparing two pitchers, such as Tom Glavine and Odalis Pérez, who have similar ERAs. Although Pérez had a slightly higher ERA than Glavine, he allowed far fewer unearned runs, and therefore was actually a somewhat better pitcher (at least before park factors are considered).
Another interesting tidbit: Greg Maddux?s ERA in 2002 clearly benefited from having arguably the best bullpen in baseball history to back him up. Braves relievers allowed only two of Maddux?s inherited runners to score all year, and both were already on third when Maddux left the game. Strangely, as can be seen on the chart, the Atlanta bullpen did not help Glavine nearly as much.
I don?t claim to be breaking any new ground with this stat. I?ve been contemplating variations on it since I was a teenager, and I?m sure others have had similar ideas before. I have no doubt that it can be improved upon, most obviously by incorporating the number of outs into the calculation for inherited runners. But this is what I came up with. It?s fairly easy to compute, and is clearly a better indicator of a pitcher?s performance than traditional ERA.
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