In parts of two seasons with the Mariners, Doug Fister showed an excellent talent for preventing walks. In 232 innings, Doug issued just 47 free passes, 1.8 per nine innings. With a low strike out rate, however, Doug's ERA came in steady at 4.11. Fister, however, may be much better than both those rates as he may not be getting calls on the low part of the plate to the catcher's throwing hand.
First, Doug does a great job of keeping the ball in the strike zone, the main reason for his low walk rate.
Batters tend to take his pitches to the right-hand side of the catcher.
Batter preferences on Fister's pitches may have led him to lose calls in his favor:
That's a huge area where Doug should be getting strikes, but instead the calls favor the batter. Interestingly, these call seldom happen with two strikes, so Doug isn't losing Ks that way. He is, however, falling behind in the count on these pitches, giving the batter an advantage. If Doug starts getting these pitches called early in the count, I suspect his ERA will improve as batters will be on the defensive more.