Way opposed to rise of sloth (3)
I believe the answer is:
via
'way' is the definition.
(I've seen this in other clues)
'opposed to rise of sloth' is the wordplay.
'opposed to' becomes 'v' (abbreviation for versus).
'rise of' is a reversal indicator (in a down clue, letters go up).
'sloth' becomes 'ai' (ai is a kind of sloth).
'ai' backwards is 'ia'.
'v'+'ia'='VIA'
(Other definitions for via that I've seen before include "Going through" , "Passing through" , "By means of" , "Roman road" , "By way of - in Latin" .)