What is a precise anatomical location on the human body, other than the groin, that is highly vulnerable to a knee strike and likely to cause immediate incapacitation?

A precise anatomical location on the human body, other than the groin, that is highly vulnerable to a knee strike and likely to cause immediate incapacitation is the 'common peroneal nerve' at the lateral (outside) aspect of the knee, just below the joint line. The common peroneal nerve is a major nerve that controls motor and sensory function in the lower leg and foot. A direct strike to this area with the knee can cause a 'neural stun', temporarily disrupting nerve function and causing significant pain, muscle weakness, and even temporary paralysis of the foot and ankle. This incapacitation can disrupt balance, impair mobility, and create an opportunity for escape or further defensive action. The proximity of the nerve to the surface and its lack of muscular protection makes it particularly vulnerable to a knee strike.