Sneaky boxing final -- punch in the middle is dirty (10)
I believe the answer is:
slatternly
'is dirty' is the definition.
(thesaurus)
'sneaky boxing final punch in the middle' is the wordplay.
'sneaky' becomes 'sly' (I've seen this before).
'boxing' means one lot of letters goes inside another ('box' can mean contain, as in to put in a box).
'final' becomes 'latter'.
'punch in the middle' becomes 'n' (I can't justify this - if you can you should give a lot more credence to this answer).
'latter'+'n'='lattern'
'sly' enclosing 'lattern' is 'SLATTERNLY'.
Can you help me to learn more?
(Other definitions for slatternly that I've seen before include "Slipshod" , "lacking in tidiness" , "In a sluttish manner" , "often in mess" , "(Of a woman) dirty and untidy" .)