I think (?) the artist might be making the point that the doughboys of WW1 paid in blood for the rights of these grossly overpaid sports diva to 'take a knee' in protest to the American national anthem.
We don't agree with you but we'll die for your right to free speech*
*Although given the racial politics of the early 20th century US I think he might have been stretching an historical point a bit too far.
I hope they get to visit the Underground Hospital and the fortifications on Guernsey and Alderney built with Russian and other slave labour under their predecessors' - maybe their grandfathers' - whips. As I understood it when visiting when my stepfather had a job there for a couple of years, those slaves dying of overwork were pushed into the concrete and left to set.