Wild fellow in charge (5)
I believe the answer is:
manic
'wild' is the definition.
(I've seen this before)
'fellow in charge' is the wordplay.
'fellow' becomes 'man' (I've seen this before).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'man'+'ic'='MANIC'
(Other definitions for manic that I've seen before include "Showing wild energy" , "On a pathological high" , "Of mental state veering from depression to excitement" , "Hectic" , "Frenetic, mad" .)