The only question "is support of of any political movement appropriate at a football match?"
There are many OTHER worthwhile movements for example physical abuse in marriage to name but one.
Should there be a roster whereby ALL movements of social importance are supported at the start of of a game.
I'm old enough to remember going to a game and the closest thing to a political statement was throwing halfpennies [farthings wouldn't fly] at the Salvo's.
I have empathy for BLM, but as far as football is concerned the point has been made and it's time to move on.