Silence leader in Africa, slightly crazy (4)
I believe the answer is:
gaga
'slightly crazy' is the definition.
(I've seen this before)
'silence leader in africa' is the wordplay.
'silence' becomes 'gag' (gagging is a kind of silencing).
'leader in' suggests taking the first letters.
The initial letter of 'africa' is 'a'.
'gag'+'a'='GAGA'
(Other definitions for gaga that I've seen before include "Barmy joke, third in cracker" , "Slangily crazy or senile" , "Slangily crazy, off one's head" , "Lady who sings" , "crackers" .)