screwball

(noun) a whimsically eccentric person. Synonyms: crackpot, crank, nut, nut case, fruitcake.

(noun) a pitch with reverse spin that curves toward the side of the plate from which it was thrown.

(adj) foolish; totally unsound. Synonyms: crazy, half-baked, softheaded. Examples: "A crazy scheme." "Half-baked ideas." "A screwball proposal without a prayer of working."