One watches Wall of Sound producer tackling a tango (9)
I believe the answer is:
Here is my best explanation:
'one watches' is the definition.
'wall of sound producer tackling a tango' is the wordplay.
'wall of sound producer' becomes 'spector' (Phil Spector).
'tackling' means one lot of letters goes inside another (I've seen this in other clues).
'tango' becomes 't' (phonetic alphabet: alpha, bravo, charlie etc.).
'spector' enclosing 'at' is 'SPECTATOR'.
(Other definitions for spectator that I've seen before include "Onlooker at game", "Witness", "Viewer", "given weekly inspection?", "Onlooker; magazine", "one found at ground?", "Observer", "weekly magazine?", "Publication" and "witness".)