Leader in equestrianism, victory key for competitive horse

• Competing horse or rider
• Competitive rider always covers slit in jacket
• Level ground, with no rain, for Badminton competitor?
• Sportsperson held hostage by eleven terrorists
• Equestrian competitor
• Horse rider always circling Tolkien creature
• Flat race without a horse

Wiktionary Word definitions in Wiktionary
n. 1 a horse or type of horse used in the equestrian sport of eventing. 2 (context equestrian English) the rider of a horse used in eventing.