As an economist, Mr. Fryer wonders if the difference between lethal force — where he did not find racial disparities — and nonlethal force — where he did — might be related to costs. Officers face great costs, legal and psychological, when they unnecessarily fire their weapons. But excessive use of lesser force is rarely tracked or punished. “No officer has ever told me that putting their hands on inner-city youth is a life-changing event,” he said, contrasting the consequences of shootings and lesser uses of force.