Performance about publicity trail (6)
I believe the answer is:
shadow
'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'.
(Other definitions for shadow that I've seen before include "Dark area, weak remnant (of something)" , "Sort of boxer - dog" , "Dark area - referring to parliamentary opposition" , "opposing counterpart" , "Inseparable companion; dark patch" .)