Place to relax before boxer’s last fight (4)
I believe the answer is:
spar
'fight' is the definition.
(sparring is a kind of fighting)
'place to relax before boxer's last' is the wordplay.
'place to relax' becomes 'spa' (as in a health spa).
'before' means one lot of letters go next to another.
'last' suggests the final letters.
The last letter of 'boxer' is 'r'.
'spa'+'r'='SPAR'
(Other definitions for spar that I've seen before include "Translucent mineral" , "Act as boxer" , "Box - girder" , "Box; various minerals" , "piece of wood?" .)