After reading the excellent UFC 172 Mini-Judo Chop: Jon Jones' Shoulder Crank by T.P. Grant I would like to add some extra information about this technique. This technique was made famous by Mike Tyson. I first noticed it in his 1999 fight against Francois Botha as you can see in the gif below. Since Glover's idol is Mike Tyson, you can see the irony in Jon Jones hurting him with one of Iron Mike's dirty techniques.
I am a BJJ practitioner and I have learned the hard way that there are two kinds of underhooks. The dominant underhooks and the "lazy" underhooks. A lazy underhook is the one where you are not pushing your elbow away from your ribs. My instructor Wander Braga catches me all the time with this technique. In Brazil they call this technique "the manivela" and they use it to catch wrestlers due to the wrestler's obsession with underhooks.
Another option is what Marcelo Garcia calls an "elbow control armbar" where he traps the hand in his armpit and turns the elbow down while pushing it up. You can get very fast taps out of this one. Thanks again for the great judo chops.