Delay playing notes by barrier (9)
I believe the answer is:
stonewall
'delay' is the definition.
(I've seen this before)
'playing notes by barrier' is the wordplay.
'playing' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'barrier' becomes 'wall' (I've seen this before).
'notes' is an anagram of 'stone'.
'stone'+'wall'='STONEWALL'
(Other definitions for stonewall that I've seen before include "Use delaying tactics as in cricket" , "Delay or block (a proposal's) progress" , "Stand firm" , "Play or obstruct defensively" , "Hold up progress" .)