I wanted to track my skill at Salsa dancing for a long time, but I never could decide on a good metric.
In some sense Anki does give you data on how well you learned facts about a subject but I wouldn't use the label "mastery".
A lot of sports do have clear metrics that you can train to improve. If you play basketball you can track your hit rate for freethrows. If you lift weight than you can track the weight.
Archery or a game like dart is also easy to track.