Dude watch the video again, he doesn't even know where he is after the fight's done. Would you rather the dude get permanently injured? I think the ref did a good job. Sure, he could have let Abe Lincoln sneak a few more in,but he was dropping bombs that were skimming Amir, once he stood he'd have gotten hurt bad.
Amir came to fight, Abe Lincoln came for blood! haha