The rudder, being a vertical variable camber wing, applies a left lift force when displaced right. The left lift force yaws the plane right and also applies a force trying to slew the plane to the left. The yaw results in the relative wind striking the side of the fuselage, creating a certain amount of lift to the right, depending on how effective an airfoil the fuselage is (some more than others). The lifting force applied to the fuselage is added to by the offset thrust line due to the yaw, also providing a lateral force to the right.
The result is the side lift of the fuselage plus the offset thrust line is more than the left side force of the rudder, and the plane slips sideways to the right, and since it's going forward as it does so it turns, although inefficiently.
It's easier to visualize if you think of an aerobatic airplane in an airshow that flies past you flying at a 90 degree bank, or flying "knife edge". The wings are completely unloaded and are doing nothing except acting like big fins. The offset thrust line of the high powered engine, and the lift generated by the plane's fuselage, is enough to hold up the entire weight of the plane, even though the rudder at the back is pushing "down" like an elevator on a flying wing.
Roll the Extra aerobatic airplane back to level flight and do the same thing, and you get a skid-turn to the right from the rudder pushing the tail to the left.