Although Toad keeps getting left out as a playable character in all the mario spinoffs (which I think is terrible, since he's my favorite character period), the evidence that Toad is actually a great golfer is not hard to find.
First off, he owns a golf course, Toad Highlands, and the trophies for said course are mini statues of Toad with a golf club. Also, he gets to make the official calls (OB, etc). Apparently he was just so good that he retired and now runs it for everyone else ;)
