The story
From (onomatopoeia) whiff (“to strike, to strikeout”) + ball. Not derived from whiffle, though both derive from same onomatopoeic sources, namely a sound of wind.
Etymology from Wiktionary, CC BY-SA 4.0.
wiffleball
Today it means: A game similar to baseball, played with a lightweight bat and ball and suitable for children to play in confined areas. Full definition →