Complaint made by 50 in club (5)
I believe the answer is:
bleat
'complaint' is the definition.
(I've seen this in another clue)
'50 in club' is the wordplay.
'50' becomes 'l' (Roman numeral).
'in' is an insertion indicator.
'club' becomes 'beat' (I've seen this before).
'l' put within 'beat' is 'BLEAT'.
'made by' acts as a link.
(Other definitions for bleat that I've seen before include "Sound made by goat" , "Cry of a sheep or calf" , "Sheep's call" , "Sound from the fold" , "Sound like a sheep" .)