I'm not sure if I understand your question.
The ball has to be fielded... most times a triple play occurs with men on first and second. A line drive is usually hit to the shortstop or to the second baseman. He catches the line drive for the first out. He then tags the runner coming off second base for the second out. He then completes the triple play by tagging the runner advancing from first base as he was moving when the line drive was hit. He has to tag the second runner coming down towards him (from first base) because stepping on the second base bag would nullify a force play. The runner advancing from first base could just run back to first base. In that case, it becomes a double play.