What’s is this about?

Does anyone know why before every start of the game there’s a line of people on the warning track? I’ve always noticed them coming onto the field during the pregame show but I’ve never heard of what’s the point?
Does anyone know why before every start of the game there’s a line of people on the warning track? I’ve always noticed them coming onto the field during the pregame show but I’ve never heard of what’s the point?