Gather popular umpire retired (5)
I believe the answer is:
infer
'gather' is the definition.
(synonyms)
'popular umpire retired' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'umpire' becomes 'ref' (short for referee).
'retired' says the letters should be written in reverse.
'ref' reversed gives 'fer'.
'in'+'fer'='INFER'
(Other definitions for infer that I've seen before include "Presume" , "come to a conclusion" , "Deduce (from evidence)" , "Deduce logically" , "Conclude by reasoning" .)