WASHINGTON, D.C. – In the small lobby at the entrance of the home clubhouse at Nationals Park, Josh Hader, still in his All-Star Game uniform, sat in a puffy chair, his head tilted down, his eyes fixed on his phone’s screen, his thumbs the only thing moving. They swiped up, left thumb then right thumb, left then right, left then right, for a minute, then two, then three, before a security guard closed the door and cocooned Hader from the throng waiting outside to ask if he was a racist, sexist, bigoted homophobe. Outside the clubhouse, about 15 feet away,...