Before eerily empty stands at Nationals Park, players from both teams dropped to one knee and together lifted a giant black strip of fabric.
As the players knelt, a message addressing social injustice recorded by actor Morgan Freeman played over the stadium speakers.
After kneeling for around 20 seconds, players got to their feet and stood in unison for a rendition of the US national anthem, “The Star-Spangled Banner.”
The United States has been convulsed by nationwide protests against racism and police brutality after the May 25 death of unarmed African-American man George Floyd in Minneapolis at the hands of officers.
Taking a knee has become a widely recognised gesture of solidarity with Black Lives Matter, adopted by protesters and professional athletes around the world in the weeks since the protests erupted.
Kneeling was first used as a gesture of protest by former NFL player Colin Kaepernick in 2016, who was widely ostracised for his protests against racial injustice.
Thursday’s season-opener in the US capital was taking place some four months after the league had initially been scheduled to get under way in March.
The start of the season was suspended due to the coronavirus pandemic.
The opening game was marked by an appearance from US infectious disease specialist Anthony Fauci, who tossed the ceremonial first pitch to get the season under way. Fauci’s pitch went way wide of the catcher.
After bitter wrangling between Major League Baseball’s team owners and players, an abbreviated 60-game season was mandated by commissioner Rob Manfred.
Games are taking place without fans while players are subject to a range of strict health and safety protocols designed to prevent outbreaks of COVID-19.
Players will be tested for the disease every 48 hours while masks will be mandatory for players on the field.
Two staples of baseball — chewing tobacco and sunflower seeds — are also effectively banned. Under baseball’s new safety code, any spitting is forbidden.
COVID-19 meanwhile struck a blow to the World Series champion Nationals earlier Thursday after it emerged star outfielder Juan Soto had tested positive for the disease.
Nationals general manager Mike Rizzo said Soto faces an indefinite spell on the sidelines as he recovers.
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