“I think taking the knee is from football.”
I don’t think you’re correct.
I think it’s far, far older than that.
Bending the knee is certainly far older, to show submission to royalty.
But in the context of Kaepernick, and sports, I think the more recent football use was what he and the players were thinking of.
Someone should ask them their view on the symbolism, history, and what they are thinking. Most would say, “Whu... I don’t know. Black Lives Matter. Team spirit.”