Fathers display travel document (8)
I believe the answer is:
passport
'travel document' is the definition.
(I've seen this before)
'fathers display' is the wordplay.
'fathers' becomes 'pas' (pa is a kind of father).
'display' becomes 'sport' (to sport an item is to wear or display it).
'pas'+'sport'='PASSPORT'
(Other definitions for passport that I've seen before include "papers" , "Traveller's ID" , "Travel identification" , "Travel doc" , "Document allowing travel abroad" .)