Pirates' Zach Duke's Recent Outings Help "True" His ERA

Zach Duke is one of the Pittsburgh Pirates' better pitchers. But he is not as good as his ERA suggests. Last night, (and in the previous two starts), this fact caught up with him: he has given up 18 earned runs in 13 innings, adding 0.70 to his ERA over that span.

An alternative, and over the long run better, measure of a pitcher's ability is his FIP, or what we call sabermetric ERA. This is based on three factors controllable by the pitcher, home runs, base on balls, and strikeouts.

There is a fourth factor at work, BABIP, or batting average on balls in play, that is presumed to be about the same for most pitchers over a long period of time (about three full seasons). But over shorter periods of time, an unusually high BABIP could raise a pitcher's ERA above his FIP, while and unusually low BABIP would lower it.

Even after his recent travails, Duke's ERA is about three quarters of a point better than Paul Maholm's. But compare their other statistics, and you can see why we think that Maholm is the better pitcher.

Although each pitcher has had 28 starts, Duke has given up 22 home runs, Maholm 14. Duke has struck out only 89 batters to 113 for Maholm. Only on Base on Balls does Duke have the advantage, 42 versus 52.

So Maholm's FIP is actually better than Duke's: 3.82 vs. 4.38. But it doesn't look that way because Maholm's ERA is almost a full point worse than his FIP while Duke's is three eighths of a point better.

We won't discuss Duke's results against Milwaukee and Cincinnati, which are basically  explainable by the four home runs and three walks (counting a balk as a walk) he gave up. But such bad pitching finally catches up with someone, meaning that Duke finally got a WORSE result than his sabermetrics, against the Cubs.

Five consecutive singles scored two runs and loaded the bases. Then back-to-back doubles scored four more runs.  An infield single and a ground out scored the seventh run (originally on second base), all in the first inning. This usually doesn't happen if a pitcher doesn't give up home runs or walks. But later on, Duke gave up an eighth run on a solo homer.

Duke typically does poorly late in the season. He ranks ninth the National League in innings pitched, which may be a reason why. So the Pirates have switched to a September six man rotation to give him (and others) some rest.

Another pitcher that is coming up, and likely to surpass Duke in ERA is Ross Ohlendorf, who had only a 3.16 ERA in August. But that was in spite of giving up seven (solo) home runs, his second highest monthly total, which suggests a high FIP.

Ohlendorf has maintained his actual late-season ERA in September, but has given up no homers so far, suggesting that his FIP may catch down to his ERA (good) rather than his ERA catching up to his FIP (bad).

But FIPs show why the Pirates, who started the season with the "best" ERA in baseball, couldn't maintain it. Such a performance was never really "in the cards" (raw statistics).