Illegal back row attack

[Raybo]

Can the R2 call a back row attack? My understanding is this is a positional penalty. What if the R1 is visually blocked in viewing the foot/feet placement (say by another player occluding the view of the foot relative to the attack line).
Is this considered good teamwork? or should the R2 'pass' on signaling this infraction. As with other sports the bottom line is to get the play 'right' and not be so concerned with who makes the call. I understand each has their primary responsibilities, however, I would be glad that the R2 has 'my back' when it looks like I either did not see the foot placement or simply missed the call. In NF, it does not seem to directly address this situation.