Originally Posted by
SoldSpartan
I was mountain biking today got tired and decided to set down for a few minutes when I got back on the rear tire wouldn't spin. Turns out the chain was jammed between first gear and that plastic ring that is between the cassette and the center of the wheel. Luckily I was able to pry the chain loose and was able to go on my way. Question is what caused this to happen and can it happen again?
You laid the bicycle down on its right side while you rested, pushing the derailleur and chain past first gear. The derailleur mount may or may not be bent.