It's a ratio of overall scoring performance. The problem with this, and if NS are awarded 15 points, the ratio becomes inaccurate (they have 15 extra goals scored, but no reflective goals against - i.e. a GD of 3, rather than -12).
The other option (which is set up now) is to simply rate teams by: (first) points; (second) goals scored; (third) goals against.
we're the ones who turned up to play here.