Clearly the old boy takes six lousy changes! (9)
I believe the answer is:
obviously
'clearly' is the definition.
(I've seen this before)
'old boy takes six lousy changes' is the wordplay.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'takes' says to put letters next to each other.
'six' becomes 'VI' (Roman numerals).
'changes' is an anagram indicator.
'lousy' anagrammed gives 'ously'.
'ob'+'vi'+'ously'='OBVIOUSLY'
'the' acts as a link.
(Other definitions for obviously that I've seen before include "of course" , "Clearly and unmistakeably" , "In an evident manner" , "Evidently, plainly" , "Manifestly, unmistakably" .)