Season's run out for variable mole activity (6)
I believe the answer is:
spying
'season's run out for variable' is the definition.
I can't judge whether this definition defines the answer.
'mole activity' is the wordplay.
'mole' becomes 'spy' (I've seen this before).
'activity' becomes 'ing' (I am not sure about this - if you are sure you should believe this answer much more).
'spy'+'ing'='SPYING'
Can you help me to learn more?
(Other definitions for spying that I've seen before include "Catching sight of; agent's job" , "collection of information" , "Bond trade" , "Acting as a secret agent" , "Working undercover" .)