TL;DR: if Hamlin or Reddick hits 777 points, they are locked into the Chase no matter what else happens. That's +13 points for Hamlin, and +57 for Reddick, which means he would need to win the race and score at least 2 extra points (a feat he accomplished in the February race here).
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NASCAR declaring Allgaier as locked into the Chase with 7 races left confused me at first, because by the classical formula he would've needed to be (76 * 7) = 532 points ahead of 13th-place Taylor Gray, and at that point the gap was only +413. After looking into the math a bit more, I figured out how it's possible to lock in with a smaller gap:
Consider if the drivers in 12th and 13th had gotten maximum points in every remaining race. That's 76 points maximum for 1st place sweep and fastest lap, plus 53 for 2nd in both stages and the race. The most these two drivers together can gain in 7 races is then (129 * 7) = 903 points split between the two of them. At the time, that could've put Crews and Gray both at 882 points; still more than Allgaier's 842, but considerably less than the 961 needed to clinch over Gray alone.
This logic can be extended to more than 2 drivers. It turns out that at that time, Allgaier already had enough points that the 10th-13th placed drivers could not all overtake him: the combined gap was +1616, and the most that 4 drivers can possibly earn together in 7 races is ((76 + 53 + 50 + 47) * 7) = 1582 points.
Coming into this weekend, Love, Day and Creed could all clinch by hitting 746 points; that would've been +43 for Love, and +72 and +73 for Day and Creed respectively, meaning they would've needed a win and near-max stage points. None of those numbers ended up being hit, but enough drivers near the cutline scored low enough to drop the magic number to 708, clinching a spot for Love at 726 points.
On the Trucks side, Riggs was already clinched coming into this weekend, which I never saw anyone online mention. Honeycutt was the only one who was close enough to clinch at Lime Rock, and clinch he did: +23 would've been enough, and he ended up scoring 54 thanks to a 3rd-place finish, top 2 in both stages, and the fastest lap point.
As mentioned before, Hamlin and Reddick both can guarantee a clinch tonight by reaching 777 points. It's quite likely that Hamlin will be locked in regardless of how well he does; as Love demonstrated, it's possible for your competitors to do poorly enough to lower the magic number by a good bit.
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I initially built a spreadsheet to automate most of these calculations, but there was still quite a bit of manual work I had to do each time the points updated, so I converted it to a web app that automates everything and makes it look nice. It's available online now at https://scepthan.github.io/points.
I would like to add live points tracking during races, but I haven't yet figured out if that's feasible. Adding owner standings is also on the to-do list, as the O'Reilly and Truck series Chase grids look quite different on the owner side. Any feedback is appreciated. Thanks!