Confesses it's mad to mess about (6)
I believe the answer is:
admits
'confesses' is the definition.
(I've seen this before)
'it's mad to mess about' is the wordplay.
'to mess about' indicates an anagram (I've seen 'messed about' mean this).
'its'+'mad'='itsmad'
'itsmad' anagrammed gives 'ADMITS'.
(Other definitions for admits that I've seen before include "grants us access" , "Takes in" , "Confesses or allows to enter" , "Owns up or grants entrance to" , "Concedes" .)