Rioters have looted stores and thrown rocks and bricks at Baltimore police in the wake of the death of Freddie Gray, who died in police custody. The epicenter of the protests is less than a mile from the ballpark.
About 1,000 spectators were in the stadium when the game was called off, and many gates already had been closed.
The St. Louis Cardinals said that ace Adam Wainwright is out for the season because of a torn left Achilles' tendon.
General Manager John Mozeliak said that Wainwright will have surgery this week.
Wainwright was injured while batting Saturday in Milwaukee.
Max Scherzer will not make his scheduled start for the Washington Nationals against the Atlanta Braves on Tuesday night because of a sprained right thumb.
Manager Matt Williams said Scherzer may be ready to start "before another five days."
Scherzer jammed the thumb while batting against St. Louis on Thursday.
Kansas City Royals pitcher Edinson Volquez has dropped his appeal of a five-game suspension for his involvement in a brawl with the White Sox last week.
Volquez was to start serving his suspension against Cleveland on Monday night. He is eligible to return Saturday when the Royals play Detroit.
Marlins cut Jarrod Saltalamacchia
Catcher Jarrod Saltalamacchia was designated for assignment by the Miami Marlins.
Saltalamacchia signed a $21-million, three-year contract as a free agent before the 2014 season. He batted .222 last season with a slugging percentage of .357, worst among regular catchers, and committed 15 errors, most by a catcher since 2003. This year he is two for 29 (.069) with 12 strikeouts.
The Marlins will try to trade Saltalamacchia.
Ryan Braun sits out Brewers game
Ryan Braun was out of the Milwaukee Brewers' lineup, part of Manager Ron Roenicke's effort to get more from the team's struggling offense.
Roenicke said that Braun was healthy enough to play, but was getting a second consecutive day of rest.
Braun had soreness in his right side earlier this season. He is batting .230 with one home run and four runs batted in.