If you have selected Fantasy Points as your league scoring type, only those categories measured in raw numbers can be selected as a scoring category.

Categories such as batting average, ERA, WHIP, slugging percentage, etc. cannot be used as scoring categories, because it is not possible to apply a point modifier to these values.

If you have used these categories in the past and would like to incorporate them into your current league, you should change your league settings to Rotisserie or Head-to-Head scoring.