There's a score on Splatoon2 which only appears before you play Turf Wars,
The rules seem to be roughly:
If you win a lot of games, it goes up slowly
If you lose games, it goes down very quickly
For example, I won 10-15 games of Turf and it got up to about 20. However I then lost one game, and it decreased all the way to 12.
I think (but I'm not certain) your individual play seems to affect it as well as win/loss. (I don't know what affects it - kills? coverage?)
I think (but I'm not certain) if you have a DC on your team it does not go down when you lose (same as in Ranked)
Finally I do not know the proper name of this score.
Does anyone know the actual rules of this score?