I gave up trying to figure that out a long time ago. Illegal binding, turning, front row collapsing/angling/standing. I wish they’d just pause the clock after the first failed scrum and maybe go back to the previous rule(engage, etc.) but that’s never going to happen. Even though it’s often an inscrutable part of the game it’s still intensely exciting. See Toulon-Racing when Tomafuna(spelling?) was subbed back in near the end. Geez it doesn’t get any better than that.