This is about how teams are defending the 49ers outside zone run game using a 5 man front, but with a slight variation from a typical 3-4 front. Teams are putting DTs inside of the OTs while putting their outside LBs outside of the tackle box. This is the first snap from the GB game.
The 49ers like to bring their WRs in close with reduced splits to help the run game. By bringing in the WRs, the 49ers are saying "the edge is not the OT or inline TE, the edge is the WR that is in the reduced split". Defenses are countering this by placing OLBs head up on the WRs.
Notice #91, he's not aligned outside of the TE, he's aligned head up on the WR. Now that WR can't crackback on him to seal the edge.
Not all situations are what I described above, but it's similar enough to see a trend. The two red OLBs are way outside of the tackle box. The three DTs are either head up or inside of the OTs. Those two OLBs are dead set on not being pinned to the inside. (first run play vs GB)
49ers try outside zone and GB is able to string out the run. Forget that Mack got blown up, watch the OLB #91. When #91 sees Juice motion presnap, #91 gets even wider in his alignment. He's not allowing any blocker to outflank him.
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This is the second run in the GB game. This is a better illustration of what was mentioned above. Three DTs inside of the OTs, two OLBs way outside. 49ers will run outside zone using Deebo to try and capture the edge with speed.
The play is again strung out to the sideline. This is better example of why defenses want to clog the middle with three DTs. It keeps the LBs clean and able to flow to the ball while the OLB to the playside has an alignment that prevents the edge from being sealed. Looking at this from the all22 view, you can see where the weakness is in the D front. I'll break up this post up to show how the 49ers are trying to counterpunch this.