Seamen hit rocks, struggling with this? (9)
I believe the answer is:
mainsheet
'struggling with this?' is the definition.
The definition suggests a singular noun which matches the answer.
'seamen hit rocks' is the wordplay.
'rocks' is an anagram indicator.
'seamen'+'hit'='seamenhit'
'seamenhit' is an anagram of 'MAINSHEET'.
(Other definitions for mainsheet that I've seen before include "front page?" , "Some tackle" , "Sailors' rope" , "One adjusts canvas" , "Crafty line" .)