Answer: bestrides

AnswerCrossword Clue
BESTRIDESStraddles.
BESTRIDESMounts a horse.
BESTRIDESStraddles
bestridesSit astride on
bestridesBESTRIDE, to straddle (to side, stand, or walk with the legs far apart)
bestridesStand astride over; span or straddle