Happen to see fellows over time in particular area (9)
I believe the answer is:
catchment
'particular area' is the definition.
'happen to see fellows over time' is the wordplay.
'happen to see' becomes 'catch'.
'fellows' becomes 'men' (I've seen this before).
'over' is a charade indicator (letters next to each other).
'time' becomes 't'.
'catch'+'men'+'t'='CATCHMENT'
'in' acts as a link.
(Other definitions for catchment that I've seen before include "drainage basin" , "collection of water" , "Area from which school's pupils are drawn" , "Area from which river derives its flow" , "collecting water" .)