In MLB regular-season extra innings, each half-inning starts with a runner already on second base. The rule creates immediate scoring pressure, but it also raises questions about who the runner is, whether teams can pinch-run, and how runs are charged.
If the No. 7 hitter is due to lead off the inning, the No. 6 spot in the batting order is placed on second base unless a legal substitute or pinch-runner is used. This keeps the runner tied to the lineup rather than letting the offense choose any player for free.
The automatic runner is an MLB regular-season rule. Postseason games use traditional extra innings, so teams must earn their baserunners from the start of each extra frame.
If the automatic runner scores, that run is not charged as an earned run to the pitcher simply because the runner was placed on second. Other runners and later scoring still follow ordinary official scoring rules.
Because a runner starts in scoring position with no outs, the inning often turns into a run-manufacturing problem. A bunt, stolen base, productive ground ball, sacrifice fly, or contact play can decide the game quickly.
The offensive team may replace the designated runner with an eligible substitute, but that is not a free choice created by the extra-inning rule. The substitute enters the game under normal substitution rules, occupies the replaced player's lineup position, and the removed player cannot return in MLB. A player already in the game in another batting-order spot cannot simply move to second. The automatic placement therefore creates a tactical choice: accept the scheduled runner or spend a bench player for more speed while accepting the later lineup consequences.
For earned-run accounting, the automatic runner begins the inning as though reaching second because of a fielding error, without charging an actual team error. If that runner scores without an intervening defensive error, the run is generally unearned against the pitcher. A different runner who reaches through a hit, walk, or other ordinary event is evaluated normally. Unearned does not mean the run is excluded from the game score: it can still decide the result and is credited as a run to the player who occupied second.
The visitor begins the top of every regular-season extra inning with its designated runner on second, and the home club receives the same placement if the bottom half is needed. If the home team takes the lead in the bottom half, the game ends under ordinary walk-off rules; it does not need to record three outs. If the score remains tied, the process repeats in the next inning with a newly determined runner based on the upcoming lineup position.