Baseball base-running rulings often turn on one detail: whether the runner had to advance or could choose. That difference decides whether the defence can touch the base, must tag the runner, or needs an appeal.
On a force play, the defence can retire the runner by controlling the ball and touching the base the runner is forced to reach. If the force disappears first, the defence usually has to tag the runner instead.
A run cannot score if the third out is a force out, or if the batter-runner is put out before reaching first. On appeal plays, the timing and type of the appeal can decide whether a run counts.
With runners on first and second, a ground ball initially forces both runners forward. If the defence first retires the runner from first at second base, the runner who began on second is no longer forced toward third because the trailing runner no longer needs second. A later play at third must tag that runner rather than merely touch the base. Reverse the order and touching third while holding the ball retires the still-forced lead runner. This changing chain is why umpires identify the exact sequence of outs instead of labeling the entire batted ball a force play.
A runner may leave the base as soon as a fielder first touches a fly ball, even though the catch is not completed until control is established. If the runner leaves before first touch and the ball is caught, the defence can appeal by clearly indicating the violation and touching the original base while holding the ball, or by tagging the runner. The appeal must occur while the opportunity remains under the rules, generally before the next pitch or intervening play. Until a valid appeal is made, the umpire does not ordinarily volunteer the out.
A runner failing to retouch after a caught fly is out on appeal, but that is not automatically a force out. A run crossing the plate before such a third out can count, unless another run-scoring exception applies. By contrast, no run scores when the third out is a force out or when the batter-runner is retired before touching first. On a play with action at several bases, record when the run crossed, which runner made the third out, and the legal type of that out. The label, not merely the location of the base touch, decides the scoring rule.
That may not matter if the inning ended on a force out before the run legally scored. Baseball does not only ask who crossed first; it asks what kind of out ended the play.