Slip by youngster carrying pole (4)
I believe the answer is:
skid
'slip' is the definition.
(skidding is a kind of slipping)
'youngster carrying pole' is the wordplay.
'youngster' becomes 'kid' ('kid' can be a synonym of 'youngster'**).
'carrying' says to put letters next to each other.
'pole' becomes 's'.
'kid' put after 's' is 'SKID'.
'by' acts as a link.
(Other definitions for skid that I've seen before include "Slip out of control" , "Runner" , "lose control momentarily" , "Slide fast" , "Slide at an angle" .)