Possible Clues:

• On a seat grasping Trigger's flanks?
• Get right into a seat -- with legs thus?
• Upon a seat gripping Trigger's flanks?
• Turn red, sat awkwardly on top with a leg on each side
• With legs stretched widely on each side of
• With a leg on either side of (something)
• Keeping members apart, answer's to adopt a non-committal attitude
• A seat keeping ends of their legs apart
• How the jockey wants to be? Starts with the rider getting into a seat
• Sat awkwardly on rickety ladder with legs wide apart