The end of the game for a fellow-worker (4)
I believe the answer is:
mate
'worker' is the definition.
(mate is a kind of worker)
'the end of the game for a fellow' is the wordplay.
'the end of the' says to take the final letters.
'for' means one lot of letters go next to another (I've seen this in other clues).
'a fellow' becomes 'mat' (I can't explain this - if you can you should believe this answer much more).
The final letter of 'game' is 'e'.
'e' after 'mat' is 'MATE'.
Can you help me to learn more?
(Other definitions for mate that I've seen before include "Spouse or informal friend" , "Fellow worker" , "Friend; chess move" , "Friend, partner" , "tea" .)