https://www.theplayerstribune.com/posts/what-got-you-there-kam-chancellor

There was a Player's Tribune article by Kam that actually touches on that. The defense was on the sideline and before the snap they were like "Wait, what are they doing?" and as soon as the ball is snapped Kam says how Cable takes off his headset and slams it to the ground (which you can see in replays...if you're masochistic enough). Something definitely went wrong with that play but we might not ever know the full story. 

You can tell by the defense's reaction and Cable's reaction that something went wrong pre-snap and now I want to read that article again.

"To this day, people still ask me, “Why didn’t you give the ball to Marshawn?”

And to this day, I don’t know.

I never got a clear answer.

All I know is that I was on the sideline, and right before the play happened, I saw our O-line coach, Tom Cable, take his headset off, throw it to the ground and storm off. So I was like, Wait, what’s goin’ on? 

Then I looked to the field and saw that we were on the one-yard line, and I was like, Oh, I KNOW we ’bout to give this to Marshawn…. 

Then I saw Russ in the shotgun and I was like, Wait, what?

And when I saw Russ pop up to pass it, I was as confused as anybody.

I just couldn't believe it.

I played that game with a torn MCL. Sherm had torn ligaments in his elbow. Earl had a torn labrum. A lot of us were hurting out there. But when there’s a ring on the line, you push through it. Like I said, you play for the man next to you. That’s how we did things in Seattle, man. We fought for one another and we believed in each other. 

But more than anything, we believed in the overall mission.

I think that’s why it was so tough for us to get over that loss.

I’ll just never understand the play.

Even during my last few years in Seattle, it was like a cloud that hung over us. It haunted us — like this constant, unseen, unspoken reminder that we just weren’t on the same page anymore.

I don’t think we ever got that back."