I guess they probably get good at telling after watching many, many, many pitches. Because otherwise, you've got ONE person making a judgement call on every pitch of the game.
for the most part the batter makes the first judgement. and his/hers skill (and the other player's too, like pitchers and defense and base runners) overwhelmingly determines the outcome of nearly every game.
non-sports outcomes are always determined by judge's opinion.
have a good nite. :smile: