This will show How Seattle scored their first TD
Seattle loves the zone stretch run to the left side. Here they line up with 3 receivers to the left and the TE on the line to the right. The niners show a quarters coverage look which brings Carlos Rogers in tight.
Seattle goes stretch run to the right and Ray McDonald(highlight by the red arrow) doesn't stay at home, trying to collapse down. Lynch reads McDonalds collapse and cuts back to the open area for a 6 yard gain
From the endzone you see how this leaves a blocker to hit willis and how much of a hole is opened. Rogers and Brooks end up making the tackle.
Seeing McDonald collapse, Seattle runs the exact same play with 2 differences. The niners show the same defense, and the hawks show 3 receivers to the left, but this time they have a tight end in the slot with a receiver out right. This pulls Carlos Rogers out wide.
Again McDonald collapses down on the stretch left play. This time, Seattle runs Wilson out right to pull Brooks out, since the previous play Brooks and Rogers made the tackle, Seattle removed them from the play. You can see the gaping cutback lane for Lynch, who takes it in for the score.
It is worth noting that after that play McDonald played much more disciplined against the stretch run.
When the Niners play sound, fundamental defense they are great. McDonald should stay at home to the outside shade of the lineman, he's trying to cover the gap responsibility of Bowman.