Deeper, darker emotions had already stirred inside Cubs reliever Carl Edwards Jr. when he got demoted to Triple-A Iowa earlier this month. He could understand the baseball reasoning behind the move, the need to clear his head and reset his pitching mechanics in the minors. But what he saw on social media leading up to that decision went beyond the standard criticism of a player’s performance. It reached the level of hate speech.



Amid his early-season struggles, Edwards received racist messages on Instagram that have drawn the attention of Major League Baseball, Cubs officials and the players’ union, multiple sources told The Athletic.



“We are aware of the situation,” an MLB spokesperson said Monday. “We have a team that works with social-media companies to take appropriate actions in situations like this.”



At major-league stadiums across the country on Monday, the baseball industry celebrated Jackie Robinson Day. Players,...