Top Definition
The phenomenon of shrinkage apparent in the male genitalia during and immediately after participation in physical (usually sporting) activities.
“Bloody hell Brian, you’ve got a knob like a pre-pubescent schoolkid! What's going on?”

"Oh don’t worry about that, I’ve just got back from a 5 mile jog and I’ve got a proper Sportsman's Willy”
by Beztheowl July 29, 2009

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