MLB said it supported its players' decisions not to play as they fight racial injustice after three games were postponed on Wednesday.
Teams and players in North America have boycotted several games across different sports over the police shooting of Jacob Blake, a black man, in Wisconsin.
Blake was repeatedly shot in the back by police, prompting nationwide protests within professional sports.
The MLB clashes between the Milwaukee Brewers and Cincinnati Reds, Los Angeles Dodgers and San Francisco Giants and Seattle Mariners and San Diego Padres were called off.
In a statement, MLB said it supported players who opted not to play.
"Given the pain in the communities of Wisconsin and beyond following the shooting of Jacob Blake, we respect the decisions of a number of players not to play tonight," it said.
"Major League Baseball remains united for change in our society and we will be allies in the fight to end racism and injustice."
After all three of Wednesday's NBA playoff games were postponed, MLS had five fixtures called off and MLB three, while two-time grand slam champion Naomi Osaka is skipping her Western & Southern Open semi-final scheduled for Thursday.