Walk rate represents the frequency with which a pitcher walks hitters, as determined by total walks divided by total batters faced. It's an important tool for assessing a pitcher's capabilities and perhaps the most important in judging a pitcher's tendency to walk batters.
Walk rate is often preferred over BB/9 as an evaluative metric because it shows us precisely how frequently a given pitcher allows walks.
Obviously, one of a pitcher's primary goals is to avoid putting hitters on base, and by walking hitters, he's doing just that. Unlike batted balls -- where the outcome is largely a result of team defense and luck -- walks are a surefire way to allow baserunners.
Because of this, pitchers with high walk rates tend to struggle. However, there are a few pitchers who can get by with high walk rates because they also record high strikeout totals and keep hitters off the bases.
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