1. Some pressed wrong sell, MDC or MDCO or MCD
2. Some bought on margin and as the stock fell, it met automatic sell.
3. Some Hedge fund sold to buy or sell and cover losses
4. If is it a real problem stock will slide again.
5. If it was one day event it will find support around these levels
6. Derivatives: Some had a long-term option buy at 30, and when stock fell the intuition must sell to buy at lower price.
I am very busy, but please have a stop loss ready, if it moves up in the morning, with high volume, then raise the stop, if moves down on low volume, be careful for more stop loss order sell. It had a big run up.
Looking at the volume it is obvious somebody jumped ship--all at once. Hopefully it is not some bad news leaked to a big holder of stock and they decided to bail at any cost. Could mean the stock will get pounded in the next few weeks IF that is the case. Might be something else, but no matter such moves are not a sign of a healthy situation.