As more cities, states and businesses require customers to cover up in stores, face coverings have become a flashpoint in the debate over how to stop the spread of the coronavirus. Some opponents of forced shutdowns and social-distancing requirements are flouting mask mandates, leaving grocers, drugstore chains and big-box retailers to weigh public-health requirements against the risk of putting their workers in harm’s way.

This month’s fatal shooting of a security guard in Flint, Mich., following a face-mask dispute with a customer is the most extreme case of violence around the issue, but it isn’t an isolated incident.