She got punched and had her purse stolen. What makes you think this is an instance of the "knockout game" and not just a mugging? You seem to be double-counting the evidence, just like fubarobfusco describes in this comment.

The other examples discussed in that article are a little more credible, since it appears there was no robbery involved in many of them. Still, I'd like to know whether the rate of such unprovoked and apparently motiveless acts of aggression has actually increased recently (coinciding with the supposed prevalence of this game), or whether this is just the availability heuristic at work. I suspect the latter.

My current assumption is that "knockout game" is ginned-up "whats-wrong-with-the-youth" moral panic of the sort we've seen a number of times before ("superpredators" and "rainbow parties" being two examples that come to mind).