After entering the race course track for the post, a horse shall only be declared by the stewards when they consider such horse unfit to run in the race. No horse determined to be a starter shall be excused or declared from the race. Any horse which breaks through the gate or runs off without effective control shall be examined by the racing veterinarian and determined to be fit to compete before being permitted to start.
Cal. Code Regs. Tit. 4, § 1697