OBR 5.09(c)

Appeal plays

Some outs never happen unless the defense asks for them. Missed bases, leaving early on a fly, and failing to touch home are not called by the umpire on his own — the defense must appeal before the next pitch or play.

Key points

The umpire stays silent until the defense appeals: tag the runner or the missed base while the ball is live, or make a dead-ball verbal appeal.
The window closes at the next pitch, the next play, or when all infielders have left fair territory at inning's end.
A successful 'fourth out' appeal can replace a different third out to erase a run.
Missed home plate is special: if the runner never attempts to return, the defense can appeal by touching home.

In a game

Walk-off celebration, runner from first cuts the corner at second on the game-winning hit.

Ruling · If the defense notices and appeals at second before leaving the field, he is out — and if it is the third out, the winning run can come off the board.

Why it moves the scoreboard

Appeals can manufacture or erase runs after everyone thinks the play is over — the inning is not truly over until the defense leaves the field.