So it seems like this happened in a grocery store in Canada, the Great White North. I'm not completely sure where in Canada this is. But as you can see in this video, the thief tries to steal something (potato chips?) inside the grocery store. He is confronted by someone in a backpack, who turns out to be an undercover security for the store.
Turns out the security is a BJJ purple belt, according to Rener Gracie.
As the kid tries to throw punches to get away, the security guy quickly clinches with the thief, takes him down with an outside trip, and then quickly transitions to a back take with one hook in. Then it is pretty much over for the thief from there. Watch the video below to see for yourself.