OK,
The pic I posted was of someone wearing sneakers with socks. He slipped on sand in the road, went wide and off into a field. Both sneakers were thrown off his feet and his foot was trapped under the bike at the time of the crash. I don't have any pics of feet after crashing with proper riding boots on probably 'cause there is not injury to document. I don't know if that is helpful to you in drawing conclusions from that.
I have personally witnessed on two occaisions riders having sneakers thrown off their feet in a crash. I'm not a fan of sneakers while riding. So much so that I have turned down requests for rides from some very lovely women specificly because they did not have proper clothes for riding.
Regarding riding while covering brakes, it has been my habit for decades to cover the front brake and don't think I'll be changing that. I have had experence with covering with one finger that in an emergency stop I ran out of lever trapping my other fingers under the lever. It was a bit more exciting that I wished to have to disingate the brake so I could grab with all four fingers. Since that time my habit has been to cover the front brake with two finger on modern bikes, and all four if the bike is old enough to have drum brakes.
Interestingly enough regarding covering the clutch lever I had to adjust when I got the MP3. It also resulted in a couple of interesting moments when having to make an emergency stop, I had the habit of also pulling in the clutch (i.e. rear brake lever) For that one I have had to learn a new trick.
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