Periodically competitors are confused about the line "trainer" on the entry blank. When entering a show, the trainer is the person responsible for the care of the horse. This person may or may not be the horseperson who actually taught the horse or rider to perform at the level they are entered.
The trainer must be on the grounds during the show and a rider under the age of 18 may not be listed as trainer. Should the horse be drug tested during the show and found to be competing with the aid of an illegal medication, it is the trainer who will be held responsible and subject to any reprimand issued by USEF.