Everyone taken in by most of band's sensational publicity (8)
I believe the answer is:
'sensational publicity' is the definition.
(I've seen this before)
'everyone taken in by most of band's' is the wordplay.
'everyone' becomes 'all' (all people).
'taken in' means one lot of letters goes inside another.
'most of' means to remove the last letter.
'band' becomes 'hoop' (hoop is a kind of band).
'all' inserted inside 'by' is 'bally'.
'hoop' with its last letter taken off is 'hoo'.
(Other definitions for ballyhoo that I've seen before include "song and dance" , "Extravagant publicity or fuss" , "Brouhaha" , "Noisy or sensational publicity, hype" , "Exaggerated fuss" .)