Skiver taking against one on a slippery slope (5)
I believe the answer is:
skier
'one on a slippery slope' is the definition.
(I've seen this in another clue)
'skiver taking against' is the wordplay.
'taking' suggests deleting specific letters (take can mean remove or delete).
'against' becomes 'v' (abbreviation for 'versus').
'skiver' with 'v' taken out is 'SKIER'.
(Other definitions for skier that I've seen before include "Winter sports athlete" , "he's possibly going downhill quickly" , "Sportsman who glides over snow" , "High ball; Alpine sportsman" , "Sport exponent" .)