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I managed it. Once, ever. Of course it was travelling at 50kph downhill in the dark with a bunch of roadies :]
I'd hit a lump and my hamster-wheel-cadence meant I pulled the chain over the cog, jamming it between cog and hub flange and spokes. It locked the back wheel for a moment whilst the chain broke (and I shat myself).
It's a reason to keep track-slack on the flat and/or track.
It was repared with a chain tool (a mates, I don't usually carry one riding fg/ss).
Ftfy