Crazy general’s assistant enthralled by chart (6)
I believe the answer is:
madcap
'crazy' is the definition.
(I've seen this before)
'general's assistant enthralled by chart' is the wordplay.
'general's assistant' becomes 'adc' (aide de camp, assistant to a military officer).
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'chart' becomes 'map' (synonyms).
'adc' going inside 'map' is 'MADCAP'.
(Other definitions for madcap that I've seen before include "Eccentric or reckless person" , "Given to reckless behaviour" , "Hothead" , "Crazy fellow" , "Lunatic" .)