Its one of the worse sports injuries because it takes so long to heal. It used to be the kiss of death for professional athletes but more and more lately have been able to come back and still be their normal selfs. They sew it back together. It can't really be explained how it happens either.  It is more common in explosive sports like basketball and football.

Last years Super Bowl this freak athlete tore his Achilles running onto the field
https://m.youtube.com/watch?v=fuGwNXJ-LlY&t=0