It may be somewhat voyeuristic, but I periodically head over to YouTube to check out if there are any new videos of athletes getting an Achilles Tendon rupture. They hurt you to watch them. Here are a few:
For more on the Kevin Durant rupture, see this write up. One thing I do find interesting about Achilles Tendon Ruptures is that if you follow the literature, the outcomes between surgical outcome versus conservative care outcomes are about the same; so how does clinician make a decision as to which is the best approach? There is this very log thread on Podiatry Arena with all that literature (you can sign up to watch that thread and get notified of new updates). Some research can be followed here.
The mechanism of action in all these videos is similar. There is a simultaneous extension of the knee and flexion of the ankle as they accelerate.