Stand up to criminal type over arithmetic (8)
I believe the answer is:
confront
'stand up to' is the definition.
(thesaurus)
'criminal type over arithmetic' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'type' becomes 'font' (font is a kind of type**).
'over' means one lot of letters goes inside another.
'arithmetic' becomes 'r' (one of the traditional three R's of education).
'font' placed around 'r' is 'front'.
'con'+'front'='CONFRONT'
(Other definitions for confront that I've seen before include "Accost, come face to face with" , "Oppose head-on" , "Face in opposition" , "Face up to (a problem)" , "Challenge" .)