Performance about publicity trail (6)
I believe the answer is:
Here is my best explanation:
'trail' is the definition.
(I've seen this before)
'performance about publicity' is the wordplay.
'performance' becomes 'show' (I've seen this before).
'about' is an insertion indicator.
'publicity' becomes 'ad' (advert).
'show' enclosing 'ad' is 'SHADOW'.