jackal starts up by doing the usual "wait for the ppu to warm up" loop, followed by initializing memory.
first, it clears all of $000~7CF.
once it does this, it checks if the game was soft reset. the soft reset marker is at $7F0-$7FF, and is just the low byte of the address:
07F0 F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF
if the soft reset test fails, the game will reset $700-7FF again, write the soft reset check bytes, and then initialize both player's scores to 0 and the high score to 5,000.
...
jackal does not, at any point that i can tell, actually use this high score value for anything. it is properly tracked by the game — it is updated if player 1 or 2's score goes above it — but it isn't actually used anywhere, or shown on screen.
