A headwind in a track race that blows in a 400 meter ellipse pattern.
An out and back with rolling hills that seems to be uphill both ways.
You are out running and are about to pass someone who is walking, running, etc., and they are on the other side of the path from you. They look back, see you, and move across the path to get in your way.
The rain storm that starts when you begin your run and ends when you finish.