A gradual pain in the hamstring is usually termed a hamstring pull or strain. This injury happens when the muscles are tight, fatigued, or weakened and are then strained by overwork. Over-training, especially if this involves repetitive movements, is a common cause of hamstring overuse strains. Overuse strains start with only a slight pain, which gradually gets worse as you continue with the activity. The problem with overuse injuries to the hamstring is they tend to recur. Even if they do not develop into an acute tear they can limit your ability to run, jump and stretch your leg out.