The problem is located in the crossing between the calf´s muscle an tendon. The problem occurs on account of a forceful extension, rupture or violence of the calf muscle. Common in sports where quick muscle stimulation is required e.g. tennis, long jump, high jump and ball games. 

Insufficient warm-up.
Short and tight calf muscles.
Strain on the calf muscle.
Violence e.g. a kick.

Symptoms
Sharp pain.
Reduced muscle function.
Swelling/discoloration
Palpation soreness.
Pain on weight-bearing.

Treatment
Analyse external internal factors.
Gradually intensified traning program.
Warming brace to increase the bloodcirculation.