Oddly enough I've never broke a bone in the dirt, but it seems like I should have several times.
The one that I will always remember was when I was 16 and just getting into racing (1992). A buddy and I were running our usual trails, but keeping a log of times, so every day we were trying to push it a litttle bit further. So, on a trail that I knew like the back of my hand, there was a fairly straight, down-sloped single track section that makes an abrupt transition from bright clearcut to a dense forest. For about half a second, you're basically blind as your eyes adjust.
Just before entering the darkness, there's a "bonus line" on the uphill side that goes around the top side of a tree, instead of the main trail that makes a little swerve to go below the tree. Well, in the interest of maintaining speed to save time, I took the bonus line faster than my skills were prepared to handle. I'm not sure exactly what happened, but the darkness transition obscured the back side of the bonus line that sent me airborn. I was able to keep it pointed in the right direction and landed back on the trail, but the body contortion required to get the tires in the right spot put me in the wrong position and my right foot twisted out of the pedal and I landed hard on the saddle.

I was momentarily unable to do anything while the bike and I continued quickly down the trail. The trail then makes a slight jog to the left around another tree, which I was now headed directly toward. I remember turning at the last second to avoid a direct endo into the tree, and just clearing the handlebar, but my shoulder took a direct hit. I don't really remember the next part, but according to my buddy, I log-rolled down the sidehill until I encountered another tree which stopped me from ending up in the creek.
