Say what may be true about a trouble starter (5)
I believe the answer is:
utter
'say' is the definition.
(to utter something is to speak or say it)
'may be true about a trouble starter' is the wordplay.
'may be' indicates an anagram.
'about' means one lot of letters goes inside another.
'starter' says to take the initial letters.
The initial letter of 'trouble' is 't'.
'true' with letters rearranged gives 'uter'.
'uter' enclosing 't' is 'UTTER'.
'what' is the link.
(Other definitions for utter that I've seen before include "State - unqualified - rank" , "Pronounce - total" , "Speak or say" , "Circulate" , "in toto" .)