A highside is a type of motorcycle accident which is caused by a rear wheel gaining traction when it is not facing in the direction of travel. For a highsider to take place, the rear wheel must first lose traction and drift out of the line travel of the motorcycle. The initial traction loss may be caused by a rear locked wheel due to excessive braking or by applying too much throttle when exiting a corner.

When the slipping rear tire suddenly regains traction it is not moving in the same plane as the rest of the bike. This causes the motorcycle to straighten up so quickly the rider is almost always thrown off, even at low speed.

Highside accidents are typically caused by over-acceleration or braking in corners, but are also a result of locking the rear brake in an emergency stop while traveling straight at high speeds, such as on a highway. Chopper style motorcycles with the front brakes removed are especially prone to highsider accidents.