Motorcycle roadracing term used to describe a crash in which the bike is leaned over while cornering
and flips back up towards the outside (i.e. the high side). A high side usually occurs when rear wheel traction is suddenly lost and the rider's panic causes him to abruptyl close (chop) the throttle. As a result, the rear wheel suddenly and forcefully regains traction, violently flipping the bike away from the direction of lean and throwing the rider skyward. Most racing injuries occur as a result of a high side since the rider has much further to fall.
The flip side of this (no pun intended) is a low side
crash. These crashes are usually minor since the rider falls off much closer to the ground.
That clueless squid lost the rear halfway through Turn 7, chopped the throttle and high sided his brand new, chromed out R1 into the hay bales.