6-8 Game Desk/Statistics

Not National League specific, however, they are reporting “top performers” on the site with a +/- rating. Does anyone know how this is calculated? Its not really explained here - Game Desk Analytics — 6-8 Sports.

Its not simply a +/- like Hockey, where it tracks your team’s goals for and against when you are in the water. Seems to add other stats. Any insight appreciated.