The official scorer never goes on the field (he typically watches from the press box), and in some cases the person's identity may be nearly unknown.
The official scorer has discretion to make judgement calls about certain aspects of the score that do not affect the final disposition of the game. For example, when a fielder fails to catch a ball in play, and the runner reaches base safely, the official scorer decides whether the ball "should" have been caught. If so, the fielder is charged with an error; if not, the batter is awarded a hit. Note that this decision can never affect the outcome of the game; the runner is safe at the base either way, and the decision of whether the fielder is charged with an error has no bearing on who eventually wins the game. The only effect is on the official statistics for players that are compiled later.
Another decision that the official scorer makes are whether a ball not properly received by (i.e. a ball that gets past or away from) the catcher is a passed ball (charged to the catcher) or a wild pitch (charged to the pitcher). A passed ball or a wild pitch is only scored if a baserunner advances as a result.
Various other decisions come into play during a game, when deciding if a batter should be credited with a certain amount of bases in an extra base hit (or was purely advancing on a fielder's choice), awarding a stolen base or defensive indifference (the runner took the base without any interest or acknowledgement of the defensive team to put them out on the play), awarding assists to fielders on deflected balls (having to decide between effective or ineffective deflection) and judging the plays involving other less common baseball quirks.
The positions on the field all have numbers (distinct from the players' uniform numbers) that are the same no matter what team is playing. That way the scorer does not have to write out # 1 batter grounded to the shortstop and the shortstop threw the ball to the first baseman; he can just write 6-3 .
The numbers and associated positions are:
- first baseman
- second baseman
- third baseman
- left fielder
- center fielder
- right fielder
See also Amateur baseball scorekeeping