There are so many possible causes for a dull ache in either leg, it would be hard to name them all. If it continues, a doctor should be consulted. It may only be a muscle spasm, but since there are...
Not counting injury, such as a blow to the groin, a strain on the tendons and ligaments in the groin can produce pain. Generally, rest and cold will help. As weird as it sounds, a bag of frozen green...