The Worst Average Seasons
Per ERA-, the worst season among Pirates' starters was 2006 Zach Duke. Duke worked to a 4.47 ERA, 4.13 FIP, and 1.5 WHIP in 215.1 innings. Like with Sisk, it's hard to believe that a pitcher can have a mid-4 ERA and not be terrible. But Duke's ERA was actually slightly better than the average as the rest of MLB had a 4.53 ERA. Nearly five runs were scored per game, on average. But once you use park factors, his ERA comes out to league average, as he had a 100 ERA+ and ERA-.
As stated earlier, there were very few average seasons per ERA- for relievers. Blas Minor had the worst among these seven, per ERA. During 1993, Minor pitched a total of 94.1 innings for the Pirates, working to a 4.10 ERA, 1.27 WHIP, and 3.26 FIP. Minor registered a 101 ERA- and 98 ERA+, but his FIP was well above the average as he posted an 81 FIP-. Keep in mind the average ERA for this season was 4.19.
The worst average season per fWAR was a hard one to decide. In 2010, Paul Maholm had a 5.10 ERA, 4.18 FIP, and 1.57 WHIP. However, because of his respectable FIP, he had an fWAR of 1.9. On the other hand, you have Ian Snell in 2006. Snell's ERA wasn't anything to be proud of either, with a 4.74 mark, but he had a far worse FIP at 4.58. Snell also had a 1.9 fWAR.
Now moving on to FIP, Murry Dickson's 1953 season is the worst. Ironically this was his one and only All-Star season, but despite that, he had a 4.53 ERA, 4.38 FIP, and 1.49 WHIP across 200.2 innings. Both his ERA and FIP were about average. He had a 100 ERA+, 103 ERA-, and 100 FIP-. The league average mark in FIP during this year was 4.14.
Among relievers, Junior Walsh has the worst league average FIP. In 1950, Walsh's next to last Major League season, the right-hander had a 5.05 ERA, 4.46 FIP, and 1.44 WHIP across 62.1 innings. Walsh's ERA was well below the average this season as he had an 87 ERA+ and 117 ERA-. Though his FIP wasn't too far off from the average, as the rest of the league managed a 4.36 mark.