A ball that lands then rolls over the foul line (as opposed to a ball that lands over the foul line) is still in play. The fielder could have scooped it up and thrown it to (perhaps) get an out, but was deprived of the opportunity. Anyone on base was basically safe to reach the next base, at least (Could they run all the way? I dunno. Maybe someone who knows the sport better can say both what could have happened, and what actually did happen)
