Doctor to evaluate
Pain, tenderness, or soreness in a testicle should always be examined by a doctor. The reason is that a guy's testicle can die if the testicle twists, thus twisting off the blood supply (called torsion).
Other causes of testicle pain
include doing sports without a jock strap, getting kicked in the groin, having a testicle infection, etc... Sometimes, an ultrasound scan is done to look for torsion.