Complex sentence: Clapton stated in the same show that he had been independently writing a tune based on The Lovin'Spoonful's "Summer in the City", and when Sharp gave him the words (on the back of a bar napkin) they fit the tune.
Split into simpler sentences: Clapton stated in the same show that he had been independently writing a tune based on The Lovin'Spoonful's "Summer in the City". When Sharp gave him the words (on the back of a bar napkin), they fit the tune.