"a trope about subverting expectations, by focusing on what would normally be a secondary character, by the conventions of the genre, without changing the story.
In an adventure/fantasy, this means choosing someone other than The Hero to be the protagonist. In a mystery, it means choosing someone other than the Great Detective to be the protagonist. In a romance, it means choosing someone other than the damsel. Etc."
Modify the current trope description to refer to both The Protagonist who is not The Hero of the story (when The Hero trope is present in the story) and someone who would not be expected to be The Protagonist. Requires the least amount of work.