How do you teach a horse to carry a flag?

Teaching a horse to carry — and remain calm while the rider carries — a flag is a multi-stage desensitization process that must be completed on the ground before any mounted flag work is attempted, because the combination of the flag's movement and the rider's body position change as they handle the flag creates a more complex challenge than either element alone. Begin with the flag on the ground near the horse while it is standing: allow the horse to sniff and investigate the flag while it is completely still, then begin moving it slowly at the horse's side at ground level. The flag at ground level and moving slowly presents a much lower level of challenge than the same flag waved overhead, and the horse's acceptance of the ground-level movement is the foundation for everything that follows. Progress to the handler holding the flag stationary near the horse's shoulder, then moving it slightly in a slow arc, then touching the horse's shoulder and neck with the flag while it is still. Moving to the flag touching the horse while slowly waving is the next stage, followed by larger and faster waves. Under saddle, repeat the same progression with the rider holding the flag: first stationary at the rider's side, then moved slowly, then waved progressively more actively as the horse demonstrates relaxation at each stage. The horse should be genuinely relaxed — with a lowered head, soft musculature, and regular breathing — before any increase in flag movement is introduced, because a horse that is tolerating the flag while showing tension is a horse that has not genuinely habituated and may react when the flag's movement changes unexpectedly. A flag waved aggressively before the horse is ready is one of the most reliable ways to create a flag phobia that requires extensive remediation.