Who calls the plays on the field for the defense?

yes I think you are right the linebcker

If you are referring to high-level football, such as NCAA or NFL, the quarterback does not call the offensive plays. The offensive coordinator does. Likewise, the defensive coordinator calls the defensive plays. The quarterback simply relays this call to the field. The defensive captain will often act as the middleman for the defense. The captain could be at any position, but he is generally a linebacker or lineman.

Yep! It’s the defensive captain (any position)... but still, all he does is relay the play to the rest of the team. The similarity with the QB is that he’s wearing an armband with a playbook.

I think it varies, but it is usually a middle linebacker. They are in the best position (center of the field, right behind the defensive line) to see what the offense is doing, and makes calls and changes as they see fit. What is cool is this year the “signal caller” on defense will get a microphone in his helmet the same way a QB does on offense.