Gag and shoot a lunatic (8)
I believe the answer is:
crackpot
'a lunatic' is the definition.
(thesaurus)
'gag and shoot' is the wordplay.
'gag' becomes 'crack' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'and' means one lot of letters go next to another.
'shoot' becomes 'pot' (I've seen this in other clues).
'crack'+'pot'='CRACKPOT'
Can you help me to learn more?
(Other definitions for crackpot that I've seen before include "Nut" , "Crank" , "Odd" , "Ludicrous" , "Idiot" .)