I don’t know how the Steelers’ staff calls the defense on game day. As DC, Keith Butler likely has the final say as to what specifically is transmitted into the headset of the defensive captain. I would guess he gets suggestions from Mike Tomlin and perhaps from Tom Bradley as well. It is a collaborative effort most likely, with each of the three having a degree of input on fronts, coverages, blitzes, and most importantly, situational defense.
It is that latter category where the Steelers have failed most spectacularly these past few games. As was well documented last week, the Steelers defensive staff was out-maneuvered by the Chargers offensive staff, who repeatedly found ways to get their faster receivers matched up in space against Steeler linebackers.