Sport for boarders at the seaside (7)
I believe the answer is:
surfing
'sport' is the definition.
(surfing is a kind of sport)
'boarders at the seaside' is the wordplay.
I cannot really understand how this works, but
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for surfing that I've seen before include "sport" , "Browsing the Internet" , "Riding waves" .)