Marvellous group initially running a song (7,5)

I believe the answer is:

amazing grace

I'm a little stuck... Click here to teach me more about this clue!

'song' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for amazing grace that I've seen before include "Hymn written by John Newton, 1779" , "knocking cricketer for six?" , "Hymn that "sav'd a wretch like me"?" , "song" , "Noted words of praise" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.