What constitutes an upset (a TeamBrunnhilde criterion)?

At the end of every season, the TeamBrunnhilde points rating is calculated for every team. This is a rating, in units of actual game points. Better teams have higher ratings than worse teams. For my purposes, an upset is a game where the team with the lower TeamBrunnhilde points rating defeated the team with the higher rating. The ratings are determined at the end of the season. Differences of a few points are common, and 'upsets' in that range are not unexpected. When differences get into the upper teens, or even 20 points or better, that is a pretty good upset.

What about upsets during the current season? If is not always obvious that a result is an upset during the season. I recall 1998-99 Bellevue girls team playing at Enumclaw. The year before Bellevue was a lackluster 5-14 with a -3.87 TBPts rating. Enumclaw had been 2^nd in state in 4A. Bellevue (being Bellevue, you know) got a transfer and a bunch of 6 foot freshmen in Alan Russell's tow. Bellevue won the game. A great shock looking at the result in early December from the King County Journal. But once the season was really underway you knew that the 1998-99 Bellevue was not at all an extension of the 1997-98 Bellevue. So judging an upset during the season (especially early) may not be reliable.