Leave? Knock back skills in small racers? (2-5)
I believe the answer is:
go-karts
'small racers?' is the definition.
(I've seen this in another clue)
'leave? knock back skills' is the wordplay.
'leave?' becomes 'go' (to go is to depart or leave).
'back' suggests the final letters.
'skills' becomes 'arts' (I've seen this before).
The final letter of 'knock' is 'k'.
'go'+'k'+'arts'='GO-KARTS'
'in' is the link.
(Other definitions for go-karts that I've seen before include "Light vehicles for racing" , "Small motor vehicles" .)