Battle with new formats prior to start of decisive card game (8,6)
I believe the answer is:
stamford bridge
'battle' is the definition.
(I've seen this before)
'new formats prior to start of decisive card game' is the wordplay.
'new' is an anagram indicator.
'prior to' is a charade indicator (letters next to each other).
'start of' says to take the initial letters.
'card game' becomes 'bridge' (bridge is a kind of card game).
The initial letter of 'decisive' is 'd'.
'formats' anagrammed gives 'stamfor'.
'stamfor'+'d'+'bridge'='STAMFORD BRIDGE'
'with' acts as a link.
(Other definitions for stamford bridge that I've seen before include "Premiership venue" , "battleground" , "battle" , "Premier League spot" .)