Time for a friendly game of football (3-6)

I believe the answer is:

pre-season

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'football' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'time for a friendly game' is the wordplay.
'time' becomes 'season' (I've seen this before).
'for' says to put letters next to each other (I've seen this in other clues).
'a friendly game' becomes 'pre' (I can't explain this - if you can you should believe this answer much more).
'season' after 'pre' is 'PRE-SEASON'.

'of' acts as a link.

Can you help me to learn more?

I've seen this clue in The Guardian.

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