Niners do this alot. They'll have Warner and Greenlaw fake an A-gap blitz and then drop in coverage. Or they'll take both of them a blitz A-B on the same side.
They'll sometimes have Hufanga on the other side also drop creating a mid tier shell.
Or have him blitz the opposite b-gap to create a 3 vs 2
I don't remember this play on whether they dropped 2 or 3 players.
but ultimately, they'll play zone underneath and man outside.
Niners run alot of Cover 1, Cover 3, Quarters.
People will mistake Cover 3 with "soft" coverage because of how it looks starting out with both outsides about 8 yards back.
But it can be an aggressive coverage and you can play downhill.
What makes the Niners really unique is Warner and Greenlaw. I don't think people understand that the Niners can do these types of blitz looks and quarters without having LBs that can actually cover. The weakness of these looks are the seam routes. And generally teams will put their best receiver in the slot in a 5 wide set to force Warner to take the seam. And guess what, he actually covers it well. 99% of LBs in the NFL can't do this. He shut CeeDee Lamb down when the Cowboys tried to do this. So instead, CeeDee was probably like screw this.. and just started to sit down. When he started to do this, this played into how the Niners wanted to play defense.
The Niner Corners aren't that great. But they can play aggressive because Warner's range is huge.. and Greenlaw is right behind him. Add that with a stout front 4 and you can almost plug an play the secondary.