Maxwell's teammates stood in a line next to him.
Since then several dozen athletes, mostly National Football League players, have followed suit, using the gesture to protest police shootings of unarmed black men and to support the Black Lives Matter movement. You can see he held his cap over his heart for the anthem.
In the wake President Donald Trump's recent comments about how professional athletes who refuse to stand for the anthem should be fired, Bruce Maxwell chose to make a statement on the field.
The Athletics released a statement on Twitter shortly after the anthem, saying they "respect and support all of our players' constitutional rights and freedom of expression". He was born in Wiesbaden, Germany, where his father was stationed in the army.
While in the minors with the Midland Rockhounds in 2015, Maxwell talked about what it meant to play in a baseball game on Independence Day: "It means a little bit more to me". "I take it a little more personal".
Maxwell, 26, is a rookie catcher who hails from a military family, and has been described as "highly patriotic" by theSan Francisco Chronicle. "I guarantee things will stop".
As the football world waits to witness the impact of President Trump's challenge to NFL players regarding the national anthem protests, a Major League Baseball player has engaged in a protest during the national anthem for the first time.
Maxwell joined the Oakland organization as a second-round draft choice in 2012.