The band director needs to communicate with the coaches, trainers, cheerleader sponsor prior to the year even starting. It is not the responsibility of the bd to make sure everyone is off the field. I cannot imagine doing that while getting your band to perform at halftime.
Bottom line, there are a few times Iíve seen a visiting band director totally take advantage of the home band. And Iíve also seen the home bd defer to the visitors. Try to communicate early in the week prior what halftime will look like. Be courteous.