Sportsman happening to join English resistance (7)
I believe the answer is:
eventer
'sportsman' is the definition.
(I've seen this before)
'happening to join english resistance' is the wordplay.
'happening' becomes 'event' (I've seen this in other clues).
'to join' is a charade indicator (letters next to each other).
'english resistance' becomes 'er' (this might be a standard abbreviation of which I'm unaware).
'event'+'er'='EVENTER'
Can you help me to learn more?
(Other definitions for eventer that I've seen before include "Showjumper" , "Jumper" , "Rider in contests" , "Equestrian competitor" , "Equestrian horse" .)