I am by no means a stat nerd or anything but I am slowly getting my head around some of these concepts. When I watched the game my first reaction was that we went into our shell a bit in the second half and that impacted Darnold and his performance. Looking at the advanced stats it tells a pretty significant story about Sam's performance in the second half compared the the first. These stats are all from https://rbsdm.com/stats/stats/ and reference EPA (Expected Points Added) per play and CPOE (Completion Percentage above Expected) for descriptions see https://ontapsportsnet.com/2021/08/11/football-stats-glossary-guidebook-nfl-advanced-metrics/. Obviously these are all based on 1 week against a pretty average Defense but I'll be keeping an eye on this going forward.
In the first half Sam played well which was represented in the advanced stats. He was 10th for EPA/Play and 5th for CPOE meaning he added the 10th most "expected points" on a per play basis and was 5th in terms of performance relative to how hard the throw was. This made his EPA+CPOE 0.241 good for 6th (Teddy had a 0.113 last year and Rodgers was no.1 with 0.212). Basically he was performing well and making tough throws at an elite level.
Now for the second half these stats drop off pretty heavily, dropping to 28th for EPA/Play and 19th for CPOE. this made his EPA+CPOE drop to 0.033 (good for 24th overall), in a cruel twist of irony Teddy's was 0.298 for the second half (4th in the league).
We can make a couple of conclusions from this either of which are concerning. The CPOE dropped pretty heavily from 17.4 to -1.8 meaning the difficulty of the throws that he was completing was low, likely meaning a lot of check downs. This indicates we were not playing aggressively or our OL was getting overwhelmed and Sam was having to get the ball out too quickly to make the throws he was making in the first half.
His EPA/Play also dropped pretty heavily, from 0.268 (1 behind Mahomes) to -0.550 at 28th (1 behind Rodgers), basically indicating he was situationally bad and was taking away points based on where we were on the field.
Overall his ranking for day was not bad but not great. 21st for EPA/Play (sandwiched between Tua and Goff) and was 9th for CPOE. His EPA+CPOE was 18th with a 0.099 (This would have been good for around 22-23 in the league last year). Interestingly if you filter out any periods where we had a 90% win probability, Sam's EPA+CPOE number goes to 0.210 which was 9th. You could argue that when the game was on the line we were the 9th best Offense in the league yesterday.
The offense as a whole was 11th in EPA/Play in the 1st half to 27th in the second half despite having the 11th Rush EPA in the second half. It is hard to base any conclusions off that other than our passing game needs to be better in the second half and that means between Darnold, Brady and the OL we need to be better in the second half of games.
TL;DR Going forward, as Sam goes we go. If he plays like he did in the first half we will have a pretty good offense and we will be a pretty good team. If he plays like he did in the second half we are picking in the top 10 again.