I actually just did this. It occurred while jumping for ball, not during the landing but while actually in the act of jumping I felt it snap. The normal doctor said it was plantar fasciitis (which is inflammation of that area) which didn't make sense to me because it happened suddenly so I went to a specialist who properly diagnosed it. He says it was likely caused by me starting and then stopping a walking regimen which probably reduced the flexibility of the ligament so when I jumped the wrong way it tore.
