Leave behind jumper for collection by servant (6)
I believe the answer is:
'leave behind' is the definition.
'jumper for collection by servant' is the wordplay.
'jumper' becomes 'roo' (short for kangaroo, something which jumps).
'for collection' means one lot of letters goes inside another (inserted letters are collected by others).
'by servant' becomes 'man' (man is a kind of servant. I am not sure about the 'by' bit.).
'roo' inserted within 'man' is 'MAROON'.
Can you help me to learn more?
(Other definitions for maroon that I've seen before include "Dark crimson" , "one equipped to make a report" , "Source of report" , "Abandon on island, or a brownish-red colour" , "Reddish-brown" .)