The Parthian shot was a military tactic employed by the Parthians, an ancient Iranian people. The Parthian archers, mounted on light horse, would feint retreat; then, while at a full gallop, turn their bodies back to shoot at the pursuing enemy. The maneuver required superb equestrian skills, since the rider's hands were occupied by his bow, leaving only pressure from his legs to guide his horse.
You wound, like Parthians, while you fly, And kill with a retreating eye.
A notable battle in which this tactic was employed (by the Parthians) was the Battle of Carrhae. In this battle the Parthian shot was a principal factor in the Parthian victory over the Roman general Crassus.
Parting shot / Parthian shot
By way of metaphor, "Parthian shot" is also used to describe a barbed insult, delivered as the speaker departs.
With which Parthian shot he walked away, leaving the two rivals open-mouthed behind him.
The term "parting shot", used similarly, may be a folk etymology of "Parthian shot", meaning the term was corrupted through common parlance, but there is little firm evidence to support this claim.[2][3]
