The gesture is a nod to the recent protests following the death of George Floyd and the push for social justice.
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The team posted a video to Twitter with the caption "#BlackLivesMatter."
Giants Manager Gabe Kapler joined the team in kneeling.
Due to the coronavirus health regulations, no fans were in attendance to see the gesture at the Oakland Coliseum, but there's been an outpouring of responses on social media.
Kneeling for the anthem was started in 2016 by former 49ers quarterback Colin Kaepernick as a way to call attention to these issues.
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The first Major League Baseball player to kneel for the national anthem was former A's catcher Bruce Maxwell, who comes from a family with a strong military background.
Maxwell talked about the decision, which he says changed his life, on ABC7's "With Authority" podcast.
You can watch the full episode here.
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