Two men pulled up alongside a car and threatened its occupants with a crowbar, but they soon discovered that a police firearms team was inside the vehicle.
The men drove off along Waterfront Way, Brierley Hill, but police caught up with them.
Two men have been arrested on suspicion of possession of an offensive weapon.
One inspector tweeted on Saturday he was still "chuckling" and added: "I'd love to have seen their faces."
Still chuckling about the two lads who pulled up alongside a car last night & threatened the occupants with a crowbar...— Simon Guilfoyle 🇬🇧 (@SimonJGuilfoyle) October 27, 2018
I'd love to have seen their faces when they discovered it was a @firearmsWMP unit! 🤣🤣🤣#2incustody 😎