Catchers have been using them for years.. you get the inside of the catchers glove pad below your thumb smacked 2, 3, 6 hundred times a day (depending on how many guys are throwing),you have to put something inside to take away the pounding.. if not.. your hand is either a callous or a big bruise..
...that's unless your talking about a thumb donut to hold the bat.. or the newer thing that goes around just above your wrist and cover the up the back of your hand up to and inclusive of your first knuckle.. Those are newer..
Do you have an image of what you're referring to?
It’s the pro hitter thumb guard. I legit do not think I’ve ever seen any of our guys ever use it until this year, and I’ve only seen it because Kwan gives it up when he runs bases.