You’ll notice that there are two different types of Pitch Type Linear Weights: total runs by pitch (which is shown as wFB, wSL, wCB, etc.) and standardized runs by pitch (shown as wFB/C, wSL/C, wCB/C, etc.). The first category is the total runs that a pitcher has saved using that pitch. However, it is tough to compare these total numbers since pitchers throw different amounts of each pitch. The second category corrects for this, standardizing the values on a “per 100 pitch” basis. In other words, when you see wFB/C, that represents the amount of runs that pitcher saved with their fastball over the course of 100 fastballs thrown. - FanGraphs Glossary
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