Hard, but having a go (6)
I believe the answer is:
trying
I believe this is a double definition.
'hard' is the first definition.
(similar in meaning)
'having a go' is the second definition.
(I've seen this before)
'but' is the link.
(Other definitions for trying that I've seen before include "Making an effort - but annoying" , "activity in court?" , "Making attempts" , "distressing" , "Upsetting" .)