How the 49ers kill defenses in the passing game with the threat of the run

The San Francisco 49ers have interesting ways of killing defenses in the passing game with run threats and pre-snap motion.

It’s a long-held belief that you need a strong run game to be effective with play-action. Not true, and it’s been proven over time that it’s not true. What you need as an offense is the threat of the run, and run looks, to displace and fool a defense into thinking you’re going to zig, when zagging is all that’s on your mind.

If you have a great run game, however, and your offensive play-designer understands perfectly how to upset defensive assignments with play-action and pre-snap motion… well, you have what the San Francisco 49ers did to the Seattle Seahawks with 14:02 left in the fourth quarter of their Saturday wild-card game.

49ers head coach Kyle Shanahan comes into a stadium with a serious advantage in this regard, because the run game he’s designed over time is one of the NFL’s most diverse and effective. In-game, the little wrinkles he throws at defenses can open things up in ways defenses just can’t stop.

The play in question was a seven-yard pass from Brock Purdy to running back Elijah Mitchell. Pre-snap, this looked like a run — the 49ers had fullback Kyle Juszczyk motioning from left to right, and left guard Aaron Banks pulling the same way. With Mitchell in the backfield, this could have easily been a run, and you can see that Seattle’s linebackers reacted completely to that idea.

Purdy’s first read was backside to receiver Brandon Aiyuk, but Seattle cornerback Tariq Woolen had Aiyuk locked down. Now, Purdy had to deal with pressure, and he rolled right to get away from it.

Seattle’s defenders missed Mitchell entirely, which gave Mitchell a wide-open shot.

“Kyle is going to make you have to defend the entire field,” Seahawks defensive coordinator Clint Hurtt said this week. “Because of the amount of weapons that he has, you have to account for everybody, so it makes it a difficult challenge. It’s not like you can rotate a coverage or do things where you can eliminate one guy, you have to defend all 11 guys out there on the field. He does a great job of scheming up, calling it, and everything else, so like I said, it’s a great challenge that we have in front of us.”

That touchdown put the 49ers up 31-17, and San Francisco put the final nail in on their next drive, with this 74-yard touchdown on a short pass from Purdy to Deebo Samuel. Again, we have Juszczyk as a motion variable — this time, moving from the formation to the backfield. And again, a fake to the running back (Christian McCaffrey this time), and San Francisco’s offense was off to the races.

Good luck to any team having to deal with this offense throughout the rest of the postseason.