Fathers game is to get a travel document (8)
I believe the answer is:
passport
'a travel document' is the definition.
(I've seen this before)
'fathers game' is the wordplay.
'fathers' becomes 'pas' (pa is a kind of father).
'game' becomes 'sport' (I've seen this in other clues).
'pas'+'sport'='PASSPORT'
'is to get' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for passport that I've seen before include "Carte blanche" , "the key to success?" , "Official document required for foreign travel" , "Authorization to go abroad and return" , "International identification document" .)