Country's athletic club taking in judo practitioner, amateur ascendant (6)
I believe the answer is:
canada
'country's' is the definition.
(Canada is an example)
'athletic club taking in judo practitioner amateur ascendant' is the wordplay.
'athletic club' becomes 'AC' (abbreviation).
'taking in' means one lot of letters goes inside another.
'judo practitioner' becomes 'dan' (ranking system in Judo).
'amateur' becomes 'a'.
'ascendant' is a reversal indicator (in a down clue, going upwards).
'dan'+'a'='dana'
'ac' enclosing 'dana' is 'adanac'.
'adanac' reversed gives 'CANADA'.
(Other definitions for canada that I've seen before include "N.American nation" , "Country with six time zones" , "North American country" , "Weight units" , "Large country" .)