I am in Athens now and this is what we experienced yesterday.
We were on the metro (Line 3). The car was quite full.
When the metro arrived at the station, one guy said, "this door does not open!" The door was stuck, and in retrospect, he must have done something to the door.
Frustrated passengers tried to go to another door and created a mini-panicky situation.
I felt something and saw a guy's hand trying to open my bag (which was placed in front of my chest), so I hit that hand.
My friend was not so lucky - some cash was taken from hers. But her bag was not open as we got off the metro, which means in that short moment of panic situation, the thief reached her bag, open, grab the cash, and close it.
We are usually very careful, but in that moment, all of us (with local people) rushed to go to another door as the metro was about to leave, so our attention to our belongings was not enough.
Lesson learned: never move your hand from your bag, and if something unusual (like this door thing) happens, be even more careful.