Substitute in side possibly taking rest at end of game (8)
I believe the answer is:
deputise
'substitute' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how they can define each other.
'side possibly taking rest at end of game' is the wordplay.
'possibly' indicates an anagram.
'taking' means one lot of letters goes inside another.
'rest' becomes 'put' (I am not sure about this - if you are sure you should believe this answer much more).
'at end of' indicates one should take the final letters.
The final letter of 'game' is 'e'.
'side' anagrammed gives 'deis'.
'deis' going around 'put' is 'deputis'.
'deputis'+'e'='DEPUTISE'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for deputise that I've seen before include "Appoint as a substitute" , "Understudy" , "Appoint as stand-in" , "Act as delegate for a person" , "Stand in for" .)