Peter concentrated prior to fight (9)
I believe the answer is:
strongbox
'peter' is the definition.
('peter' is a slang term for a safe)
'concentrated prior to fight' is the wordplay.
'concentrated' becomes 'strong' (I've seen this in another clue).
'prior to' means one lot of letters go next to another.
'fight' becomes 'box' (boxing is a kind of fighting).
'strong'+'box'='STRONGBOX'
(Other definitions for strongbox that I've seen before include "Store for valuables" , "security device at museum?" , "Safe" , "Container for valuables" .)