Thrifty spouse acquiring collar finally for boxer (8,7)
I believe the answer is:
sparring partner
'boxer' is the definition.
(sparring partner is a kind of boxer)
'thrifty spouse acquiring collar finally' is the wordplay.
'thrifty' becomes 'sparing' (similar in meaning).
'spouse' becomes 'partner' (synonyms).
'acquiring' indicates putting letters inside.
'finally' suggests the final letters.
The last letter of 'collar' is 'r'.
'sparing'+'partner'='sparingpartner'
'sparingpartner' going around 'r' is 'SPARRING PARTNER'.
'for' is the link.
(Other definitions for sparring partner that I've seen before include "Argumentative friend" , "whose attacks are helpful, in practice?" , "Ring mate" , "hits rehearsed with me?" , "jabber" .)