The most common and most likely answer to this crossword clue is the 7 letter word BOARDED
I've seen this crossword clue in The Daily Telegraph
B
O
A
R
D
E
D
Buddy explains!
The straight part
We know that "Jumped on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case jumped on = boarded.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 BOARDED mean?
BOARDED verb- To step or climb onto or otherwise enter a ship, aircraft, train or other conveyance.
- To provide someone with meals and lodging, usually in exchange for money.
- To receive meals and lodging in exchange for money.
- To capture an enemy ship by going alongside and grappling her, then invading her with a boarding party
- To obtain meals, or meals and lodgings, statedly for compensation
- To approach (someone); to make advances to, accost.
- To cover with boards or boarding.
- To hit (someone) with a wooden board.
- To write something on a board, especially a blackboard or whiteboard.
- (of a structure, such as a roof, window, etc.) wooden, built with pieces of wood