Blindside

As a verb, used mainly in North America, to blindside someone means to shock, surprise and even deceive them. This figurative usage derives from the sports of rugby and American Football where the blind side is the opposite of the open side from where most attacks are made. Hence, an attack from the blind side is more unexpected because of the relatively fewer players covering that area of the pitch. The figurative meaning is thought to date only from the late 1960s according to Merriam-Webster.