I don't really think you need someone with the "FB" designation, necessarily.

 

Whether it's a TE, OL, or even a LB or DL... as long as you can execute the play I don't think it matters.

 

Now, you're not likely to see defensive guys unless it's a specific play call (a goal line call, for example)... but for everyday FB duty, there are others perfectly capable of performing the role.

 

It comes down to what the guy labeled "FB" is capable of.  If he can do more than just FB, like anyone playing the role of FB would be asked to, then you're more likely to see one make the roster.  It's now a position filled by more versatile players.  So, whoever plays "FB" is going to have to at least keep up talent wise with the TEs and other players who are there because they can also star on special teams, block, and catch passes.  It's a fight for the last roster spot or two.  Whatever label that guy has is not significant as long as he can play special teams, block in the run game, and run routes/catch passes (and do them all well.)

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