Knock a karate expert fast (7)
I believe the answer is:
ramadan
'fast' is the definition.
(month of fasting in Islam)
'knock a karate expert' is the wordplay.
'knock' becomes 'rama' (I am not sure about this - if you are sure you should believe this answer much more).
'a karate expert' becomes 'dan' (person who has been awarded a dan in karate).
'rama'+'dan'='RAMADAN'
Can you help me to learn more?
(Other definitions for ramadan that I've seen before include "Islamic holy month" , "Muslim period of fasting" , "Muslim holy month" , "The penitential ninth month of the Muslim year" , "Month in Muslim calendar" .)