There’s a runner on first. The batter hits a ball to left field. Runner on first advances to second, hitter decides to round first and advance to second as well forcing runner on second to now advance to third. The play is made at third by tagging the base not the runner. Is this considered an out, or is the runner safe even though the hitter now occupies second base?
It's not a force out situation. You must tag the middle runner before he gets back to 2nd.
The middle runner has only one safe base to get to and that's 2nd even if 2nd is occupied.
If the middle runner gets back to 2nd then the first runner's only option is 1st.