Mike McGlamry was strolling through Atlanta’s Piedmont Park when three people on electric scooters zipped by him—and he morphed into what he called “a grumpy old man.”

The riders weren’t wearing helmets. McGlamry, who represented pro football players in a class action over concussions, pulled out his phone, shot photos of the riders, called his secretary and dictated an open letter that is now on his LinkedIn page.