The phrase comes from Sky Sports Soccer Saturday, where presenter Jeff Stelling would cut to reporter Chris Kamara at a live match. Kamara's over the top delivery of Unbelievable Jeff whenever he witnessed a goal, miss or red card became a running highlight of the show in the 2000s and 2010s. Clips spread on YouTube and social media, and the line entered wider British football slang. It is still used because Kamara's genuine shock is instantly quotable far beyond football.