The most common and most likely answer to this crossword clue is the 7 letter word WALLABY
I've seen this crossword clue in The Daily Telegraph
W
A
L
L
A
B
Y
More clues leading to the result WALLABY
- Fool holding a head of balloon animal
- Idiot’s stolen a black jumper
- Wife all over infant with no top or jumper
- Fool keeping a black marsupial
- Left party in street to get a jumper
- Method describing delivery returned by Australian player
- An iconic creature among Victorians?
- Strategy to hold party in retreat with a mammal
- Spinning some googly ball, a wily Australian character
Buddy explains!

The straight part
We know that "jumper" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jumper = wallaby.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WALLABY mean?
WALLABY noun- Any of several species of marsupial; usually smaller and stockier than kangaroos