Check out this play. (Again, sorry for link but MLB has not allowed embedding of this yet).
This is a great example of the umpires using correct timing. Amateur umpires have a tendency to call a ball foul as soon as it heads that way.
This is incorrect as before the ball reaches first or third base, fair/foul is determined by where the ball settles or is touched. Most people know this rule. By the way, home plate is in fair territory.
If ever at a game and you see an umpire waiting to call foul on an obvious foul ball – well that is an ump who had a ball once hit a rock (or like in this instance spin) and become fair again.
Assuming the umpire did not use good timing and yelled “FOUL”, right away, what happens?
Again, it depends on the code.
In high school baseball, if an umpire mistakenly calls foul and the ball hits the ground – foul ball. Sorry about your luck offense.
In college a ball that flies past first or third and is called wrong can be reversed. Other calls cannot – so this play would be a foul.
In professional baseball – you use the reaction of the players to help determine if it can be reversed. On this play, if the runner continued running, it would probably be called fair.
Confused. Well a simple way to avoid this is not to call the ball fair or foul until you are absolutely sure.
Fair/Foul Ball is covered on page 37 of RuleGraphics.