BB reference defines it as estimated TO's per 100 plays. But WIS must mean touches (by which I mean plays run through that player based on their usage, not team plays). So Harden's 18-19 40 usage season is 14.5 TOV%. Which is close to his per48 multiplied out to 100 at 13.5. Another player undrafted with 14.4 usage and 3.0 TOp48 is at 19.5 TOV%. Interesting, wonder if there are other factors besides just TO's and usage.