Question about defesive alignment and the MLB position

I am no X's and O's guy and I saw something I don't recall ever seeing before. Maybe it happens all the time and I just noticed it for the first time. On the KJ Wright int against the Vikings Barton was in between Bobby and KJ. Would that make him the MLB for that play? Bobby was still in the middle of the field but they were sort of shifted to the right with KJ close to the line. Anyway, I never noticed that alignment before and it made me curious, figured someone here could probably tell me more about it.

Disclaimer; I never played a LB position! But my view is that MLB is like a free safety for the line. Plugs holes but always reads the ball.
KJ plays weakside or strong side. They do kind of the same thing but more setting the edge instead of interior line assistance. All of them can drop in coverage if the ball or motion calls for it.
But like I said, I never played that position. I was a guy wearing the bullseye for LBers and have a ruined knee to show for it!

They move around quite a bit.

The Seahawks seem to be playing a lot of "Bear" fronts this season. They've done it in the past but they're doing it a lot more now, probably due to the personnel they have. In this front you have a NT flanked by two 3-technique DTs. It clogs the middle making it hard for the offense to double team, pull, trap, etc. It's more vulnerable on the edges but I think the Seahawks feel they can counter that with their team speed, especially when we bring in more DBs.

As for your question, in the "Bear" front you'll often see players in the traditional SAM and WILL positions stacked on the same side. Think Otis Wilson and Wilber Marshall. Hers's what it looks like:



Most people think of the Seahawks' base defense as a "4-3 Under" but we've seen less of that in its pure form. One reason might be that we don't have anybody in the mold of Red Bryant that can dominate when 2-gapping on the strong side. The 4-3 Under looks like this:



I'm actually surprised there hasn't been more talk about the use of the Bear front this year - it seems like a significant shift. If you look at the players we've brought in (Snacks, Rush, Bullard) they seem to have been chosen to fit this scheme. If Snacks can play close to what he has in the past as a 2-gapping 0-tech NT, rotating with Mone who has been good, that could really help this front. KJ seems to have taken to it as well.

No bobby is always set up to be the middle backer even though they are out of the norm. It just depends on what the formation the offense rolls out. When Barton comes in he is more suited for filling gaps and tackling...like bobby so they play off the ball and right behind d line. Same with brooks. Which now puts kj in the Irvin lb role where he plays the line of scrimmage and extra cover guy because he can handle it. In fact kjs last two games have been quite impressive playing there. Once irvin comes back or they find someone capable of playing his role(cuz irvin is done for the year) kj will slide back over the middle.

Thank you very much to each of you for replying to my question. It was very enlightening. I had never heard of a "Bear" front before.

Oh above pic is not a bear front. Maybe college style. The original bear front has bigger dline overall and all three lbs to one side. High free and only two corners. When we have Adam's we are closer to a bear front, but typically we have two many dbs on the field to be a 46 defense.