Outstanding header from Spurs' subs (4)
I believe the answer is:
dues
'subs' is the definition.
(I've seen this before)
'outstanding header from spurs'' is the wordplay.
'outstanding' becomes 'due' (an outstanding debt is due).
'header from' says to take the initial letters.
The first letter of 'spurs' is 's'.
'due'+'s'='DUES'
(Other definitions for dues that I've seen before include "subs" , "Payments made for upkeep of church" , "Subscription to a club or society" , "Membership fees" .)