High bouncing balls to the backhand that are just fast enough where you cant setup properly for them, whether its catching it early, running around it, or taking it in the air. This can be framed ground stroke that's spinning in, a kick serve that's bouncing further away/toward you than you expect, and in some cases a failed lob that you didnt catch in the air.
By the time you realize you've made a mistake by second guessing yourself you kinda have to "make it up" as you go along. I've hit some really strange feeling shots in these situations. I wish I caught some of them in video so I could see what I look like when im jumping to my left, leaning backwards, swinging almost vertically... as hard as I can... lol.
"In the 1980's two men dominated--sometimes each other, most of the time everyone else."