First rule of the fight app — don’t talk about the fight app. “Rumblr,” a pending app idea, is pitching itself as Tinder, but for brawling. Like the dating app, Rumblr users would meet strangers, but ...

The story of Rumblr—the app that helped match people who wanted to fight each other—seemed too good to be true…because it wasn’t true. As we’ve explored in this column, a pesky fact like that will ...