Gather popular judge retired (5)
I believe the answer is:
infer
'gather' is the definition.
('infer' can be a synonym of 'gather')
'popular judge retired' is the wordplay.
'popular' becomes 'in'.
'judge' becomes 'ref'.
'retired' says the letters should be written in reverse.
'ref' back-to-front is 'fer'.
'in'+'fer'='INFER'
(Other definitions for infer that I've seen before include "Draw a conclusion" , "Conclude or judge from facts" , "Insinuate" , "Presume" , "Conjecture" .)