Zany (6)
'zany' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for madcap that I've seen before include "Amusingly eccentric" , "Wild fellow" , "Camp ad (anag.)" , "Dare-devil" , "Rash person" .)
(Other definitions for off the wall that I've seen before include "Humpty Dumpty's downfall was so" , "unexpected" , "Grossly unconventional" , "How Alf left (anag) -- very unconventional" , "Implausible" .)