If a string of riders yell "stay down" or "stay" or "riders coming", don't change your speed, don't change or deviate from your line, and don't swing up(esp without looking and confirming it is 100% clear). Stay exactly where you are at the same pace and wait for the string to overtake safely. Once you think they are all through, check its completely clear, signal, and then swing up.
If your lapping weaker riders expect them to be nackered at the end of a halflap and not have the energy to go another halflap before changing, pace yourself so you don't overtake on the half/lap marker.
If a string of riders yell "stay down" or "stay" or "riders coming", don't change your speed, don't change or deviate from your line, and don't swing up(esp without looking and confirming it is 100% clear). Stay exactly where you are at the same pace and wait for the string to overtake safely. Once you think they are all through, check its completely clear, signal, and then swing up.