The new Opponent Strength Index, or OSI, is the NJSIAA’s answer to the controversy caused by the Born Power Index last year.
They’re very similar formulas, and both take into account margin of victory, and the difference between two opponents’ ratings, which Born called a “spread” or “projection.”
But the OSI will be used much differently.
Let’s use Piscataway – WCTC’s 2019 Team of the Year – as an example.
Under the Born Power Index, Piscataway’s rating would increase if it beat the projection. The higher the rating, the higher Piscataway’s playoff seeding. Thus, if they score more points and beat the projection by more points, their rating would be higher, and likely their playoff seeding, too.
Under the OSI, Piscataway’s own rating also would increase if it beat the projection. But, it’s own rating is not what determines its playoff seeding. Rather, it’s the average of the teams it plays. Therefore, there is no benefit for Piscataway to score more points.
In fact, the opposite is true. Remember, if one team goes up, the other goes down the same amount. The more Piscataway wins by, and the more they go up, the more their opponent goes down. That means Piscataway earns fewer points for beating that opponent.
So, it’s better if Piscataway wins by a smaller margin.
Let’s take a look at a hypothetical Piscataway 2019 season:
The Chiefs ended last season with a BPI of 100.3. The proposal before the NJISAA would reduce reliance on historical data by centering teams each year around a median of 60. Tams above that mark would be reduced by one-third; the opposite would be done to teams below that mark. At 100.3, Piscataway is 40.3 over the mark, reduced by 1/3 would put them at 86.9.
They open the season at home against Franklin in Week 0. At 62.3 in last year’s final BPI, they would get reduced to 61.5. Against Piscataway, the Chiefs have the edge by 25.4 points. Let’s go with last year’s Thanksgiving score, where P’way won 41-14. That’s a 27 point margin, and 1.6 above the projection of 25.4.
The OSI formula stays the same all year. Divide the margin against the projection by one-fifth. You get .3, meaning Piscataway goes up to 87.2 and Franklin falls to 61.2. Piscataway gets 61.2 points for the win. (They would get half that if they lose.)
Next up is Sayreville, which will start at 79.6 and have Hunterdon Central at home in Week 0. Let’s say they beat the Red Devils by three touchdowns and Sayreville’s OSI is now a 82.6. That puts the Chiefs as a 4.3 point “favorite.”
But Sayreville wins by a field goal. They beat the projection by 7.3. One-fifth is 1.5. Sayreville goes up 1.5 to an 84.1 and Piscataway goes down 1.5 to 85.4 Sayreville gets 85.4 for beating Piscataway, and the Chiefs get half their opponents’ value – 42.1 for losing.
The number Piscataway will be seeded on is the average of its opponents. Franklin may lose in Week 2, and drop to a 60.4. The average is a 51.3, which is how Piscataway will be ranked for playoff qualification and seeding.
It should be noted that there is no 35-point blowout cap, and it’s not needed. Here’s why:
Had the Chiefs poured it on Sayreville and won by some ridiculous number like 80, they would have beaten the projection of 4.3 by 75.7, one-fifth of which is 15.4 points. Piscataway would go way up, but Franklin would plummet to 46.1. Assuming the same result the next week, falling by .8 puts them at 45.3. Averaged with 42.1 for the Sayreville loss gives them an average of 43.7.
Beating Franklin by 35 gives Piscataway a 51.3 OSI average. Beating Franklin by 80 gives them a 43.7 OSI average.
Problem solved, NJSIAA.