He increased his pace as he came to the gate, and managed a backward kick with both heels.

This lost the rider his stirrups and left him less securely seated than he wished to be.

He dropped the reins and grasped the saddle's pommel with both hands.
He strangely seemed to consider the pommel the steering wheel of a motor car.

He seemed to be twisting it with the notion of guiding Dexter.

All might have been well, but on losing his stirrups the rider had firmly clasped his legs about the waist of the animal.