Fellow in charge is crazy (5)
I believe the answer is:
manic
'is crazy' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for manic that I've seen before include "hyperactive?" , "Pathologically excited" , "Frenzied" , "Very energetic - crazed" , "Showing wild excitement" .)