It’s hard not to take your work home. Politicians glad-hand even when they’re not campaigning; linguists struggle not to scold poor grammar; off-duty police officers scan the crowd in a restaurant for signs of trouble before they sit down. So what happens when your job involves hitting people—especially when you’re paid very, very well to hit them very, very hard? There are a lot of explanations for the crisis of violence that has hit the National Football league—and a lot of them have merit.