to attack someone (especially verbally) unfairly in a deceitful, underhand, or treacherous manner, especially when they're not present in the place or situation that it happens. (as if stabbing them in the back). See backbite
Attack (someone) unfairly, especially in an underhand, deceitful manner: “Some backstab each other and threaten to settle their differences with a punch” (Thomas Boswell)
to attack someone (especially verbally) unfairly in a deceitful, underhand, or treacherous manner, especially when theyre not present in the place or situation that it happens. (as if stabbing them in the back). See backbite