Cathy is exactly right. A few years ago I wrote a jokey post called “S-Levels for UPDs.” Here is the link: S-levels for UPDs
I’ve also reprinted that post in my blog (plug plug), at http://newyorkunicycle.blogspot.com/
My point was that there is still some confusion when we use the term UPD: Do we mean a crash, a slip-off, or something in-between? Using the system for rating tornadoes, I made a pretend system for rating UPDs. Like the tornado version, it went from level 0 to level 6, ranging from getting off on purpose (not a UPD at all) to “toe clips” (death). I mentioned some really bad crashes that my brother, friends, and I have had, tho most of us never reach level 5 (thankfully), where either the rider or the unicycle is incapacitated. I’ve never done so, tho my brother has on several occasions, as has Dustin Kelm (who broke a leg) and plenty of muni’ists who have broken their equipment.