I saw that happen once...
A buddy and me were fishing back in the cove when a guy with a runabout came in and stopped about 200' away from us. He went to the aft locker and pulled out a fairly large anchor and a bunch of rode that was all tangled up. He stood up on the seat and heaved the anchor away from the boat. By the way he was moving, it appeared that he'd had a few too many, and just as the anchor hit the water, he flipped backwards and went straight in the water! Apparently, he'd been standing in the tangle of rode and it caught his foot and drug him down! By the sound of things, it seemed like he'd hit the windshield frame or something as he went in. His friends seemed to take a second to realize what had happened and they started pulling the line back in. A few seconds later he surfaced and it was clear that he was bleeding pretty bad so I tied a fender to my anchor line, cast it off and fired the motor to go and see if they needed any help. When we got along side them, the guy was cussing a blue streak and trying to stop the bleeding with a towel. I told him I was an EMT and offered to come aboard and assess his injuries, but he told me to 'f&#k off' in no uncertain terms and his friends were of the same opinion so we just started the motor again and went back to our mooring. They sat the guy down, fired up their engine and headed for the dock, leaving the anchor behind! About a week later, we were back in that part of the cove and it was getting kind of hot so we decided to take a swim. I thought I saw something on the bottom but couldn't make out what it was, so I went and got my mask and fins so I could dive down and see what it was. (the water in this part of the cove is only about 15' deep) Sure enough, an anchor! Dug around in the mud a bit and got a hold of the rode, swam it to my boat and winched aboard a nice 25 lb fluke type anchor to add to the collection!