So the 49ers are running a screen play to Elijah Mitchell #25.
If you look at the 1st picture on the bottom left (81) Trent Sherfield is WIDE OPEN on the back side of the Defender.
Unfortunately Garoppolo doesn't see it, or is instructed to dump it off to the back by Shanahan.
If he hits Sherfield this is an Explosive Play and puts the Niners in Great Field Position.
In the bottom picture you can see 5 defenders in a circle around Sherfield who is running free at the 45 yard line.
It might have gone for a TD if he is hit in stride.
Hell of a Play design by Shanahan.