151 tuna could become unhinged (7)
I believe the answer is:
lunatic
'unhinged' is the definition.
(thesaurus)
'151 tuna' is the wordplay.
I cannot quite see how this works, but
an anagram of 'tuna' is 'unat' which is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'could become' is the link.
Can you help me to learn more?
(Other definitions for lunatic that I've seen before include "Type of fringe" , "Foolish person" , "Madman - idiot" , "Crazy" , "Insane person" .)