Disqualification from competition can occur for a number of reasons, so make sure you’re familiar with the different ways in which a rider can be disqualified to avoid making a costly mistake! Text has been taken directly from the USEF Rules For Eventing, with emphasis added by the USEA.
1. Disqualification means that a competitor and his horse(s) may not take further part in the Event. It is applied at the discretion of the Ground Jury.
2. Ground Jury may disqualify a competitor in the following cases when, in its opinion, the action constitutes unsportsmanlike or abusive conduct:
a. Allowing anyone other than the competitor to school his horse, EV108.2a.
b. Riding in the Dressage arena or in the Jumping arena prior to the actual competition, EV108.2c.
c. Riding close to Cross-Country obstacles prior to the actual competition, EV108.2c.
d. Jumping practice fences that are not flagged, EV108.3c and EV108.3d.
e. Jumping practice fences in the wrong direction, EV108.3d.
f. Jumping practice fences while they are being held, EV108.3d.
g. Jumping practice fences that have been raised above the height or beyond the spread allowed, EV108.3d.
h. Jumping practice fences at times other than those laid down by the Organizer, EV108.3d.
i. Inspecting the obstacles of the Cross-Country course before they are officially shown to all competitors, EV109.1a.
j. Inspecting the obstacles of the Jumping course when the arena is closed, EV109.2.
k. Entering the Jumping arena on foot after the competition has started, EV109.2.
l. Abuse of horse, EV111.
m. Exercising with improper saddlery, EV115.1.
n. Use of a radio or cellular phone while competing. EV116