The most common and most likely answer to this crossword clue is the 7 letter word JACKPOT
I've seen this crossword clue in The Guardian
J
A
C
K
P
O
T
More clues leading to the result JACKPOT
- Tar over grass, constructing pool
- All to win, flag best raised
- Band with penny at the end in small amount of prize money
- White ball to sink for the biggest prize
- Sailor top design gets the big prize
- All to play for, with raise to pocket
- Lift large belly for the prize
- Sailor joining vessel gets top prize
- Head back after sailor’s major win
- Lift up belly in pool
Buddy explains!

The straight part
We know that "the big prize" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the big prize = jackpot.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 JACKPOT mean?
JACKPOT noun- A money prize pool which accumulates until the conditions are met for it to be won.
- A large cash prize or money.
- An unexpected windfall or reward.
- A concentration of surface wood or fuel.
- A large accumulated point bonus, originally awarded after a long set of actions but now often easily available in multiball modes.
- (of a slot machine) To issue a jackpot.
- A difficult situation.
- A jumble of felled timber.