A reason for being shipwrecked (7)
I believe the answer is:
aground
'being shipwrecked' is the definition.
('aground' can be similar in meaning to 'shipwrecked')
'a reason' is the wordplay.
'reason' becomes 'ground' ('ground' can be a synonym of 'reason').
'a'+'ground'='AGROUND'
'for' is the link.
(Other definitions for aground that I've seen before include "on the bed" , "Beached" , "On guard (anag.)" , "having hit rock bottom, perhaps" , "out of water" .)