Good dope inhaled by excellent old racketeer! (6)
I believe the answer is:
agassi
'old racketeer' is the definition.
The definition suggests a singular noun which matches the answer.
'good dope inhaled by excellent' is the wordplay.
'good' becomes 'g' (abbreviation).
'dope' becomes 'ass' (both can mean a stupid person).
'inhaled by' indicates putting letters inside (inserted letters are inhaled or absorbed).
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'g'+'ass'='gass'
'gass' placed inside 'ai' is 'AGASSI'.
Can you help me to learn more?
(Other definitions for agassi that I've seen before include "Andre --, tennis player" , "champion of the court?" , "tennis star" , "Andre --, tennis champ" .)