Witness struggle over nude twerp (6)
I believe the answer is:
viewer
'witness' is the definition.
(I know that witness can be written as viewer)
'struggle over nude twerp' is the wordplay.
'struggle' becomes 'vie' (to vie is to struggle or contend with).
'over' is a charade indicator (letters next to each other).
'nude' means to look at the middle letters (the word is stripped of its outer letters).
The central letters of 'twerp' are 'wer'.
'vie'+'wer'='VIEWER'
(Other definitions for viewer that I've seen before include "Spectator" , "One seeing" , "Audience member" , "He surveys, or watches TV" , "One who watches, say, TV" .)