A rupture of the Achilles tendon is not an uncommon problem in sports activity and can be quite dramatic when it happens, as the calf muscles and the attached Achilles tendon play such an necessary function. It is more likely to occur in explosive activities like tennis. The real problem is that the achilles tendon and the two muscles attached to it cross two joints (the knee and the ankle joint) and if the two joints are moving in contrary directions simultaneously, particularly if abruptly (as might happen in tennis), then the probability of something failing is pretty high. The treating of an achilles tendon rupture is a bit debatable because there are two options that almost all the research shows have virtually identical outcomes.
One choice for an achilles tendon rupture is conservative and the other is operative. The conservative choice is typically putting the leg in cast that supports the foot pointing downwards a little. It can take up to six weeks to get better and after the cast is removed, there should be a slow and gentle resumption of physical activity. Physical rehabilitation is normally used to help with that. The surgical choice is to surgically sew the two edges of the tendon back together, this is followed by a period of time in a cast which is shorter than the conservative option, and is followed by a similar slow and steady resumption of sport. If longer term results are compared the final result is typically about the same, but the surgical technique has the additional potential for surgical or anaesthetic complications which the conservative strategy does not have. The choice as to which method is better will have to be one based mostly on the experiences of the surgeon and the choices of the person with the rupture. There's a trend for competitive athletes to go down the surgical pathway since it is thought that this does give a better short term outcome and get the athlete back to the sports field quicker.