Answer: astraddle

AnswerCrossword Clue
ASTRADDLEOn the fence.
ASTRADDLEMounted.
ASTRADDLERiding, in a way
ASTRADDLELater, Dad's drunkenly sitting like a cowboy on a horse (9)
ASTRADDLEWith one leg on either side of a piece of riding gear, holding tips of the reins (9)
astraddlein a straddling position
astraddleWith the legs stretched widely on each side of