Hit a troublesome titan (6)
I believe the answer is:
attain
'hit' is the definition.
(I know that hit can be written as attain)
'a troublesome titan' is the wordplay.
'troublesome' is an anagram indicator.
'titan' anagrammed gives 'ttain'.
'a'+'ttain'='ATTAIN'
(Other definitions for attain that I've seen before include "Succeed in doing, get there" , "Arrive at, accomplish" , "Gain with effort" , "Reach or achieve" , "Reach objective, get there" .)