When the safety play happened (which I didn't think was a good strategy to start with), I was shocked at how blatant the hold was. I see the point that you have to let the play continue, but that's a big loophole. If you want to kill 3 minutes, you can snap the ball to your most elusive running back, just tell every blocker to grab and bear hug the defender and hold them on the ground, and the runner can run all over the field trying to beat the one defender who isn't being held on the ground.
Now that I think about it, that would be a fun play to watch.
My ancestors fought cave bears so I could make this post.