A foul ball differs from a foul tip, which occurs when the ball makes contact with the bat, goes directly to the catcher's hands, and is caught. The ball is still alive in this situation, and a strike is added to the batter's count. If a foul tip is struck on strike three, the batter is out.
The term "foul" comes from the fact that it was once common for umpires to call for balls or strikes by saying "foul." This is no longer the case but the term has been retained to describe any ball that does not belong to the hitter. A foul ball may be fair, meaning it belongs to the pitcher who threw it, or it may be wild, if the batter can reach it before the other team can get to it.
Fair and foul balls are important parts of baseball. They can end up being hit for considerable distance given the right circumstances. For example, a fair ball that hits the ground near the first-base bag can be driven 400 feet using the fielders' leverage against big-league pitchers. Similarly, a foul ball that misses the bats by a few inches could be hit 500 feet if it lands in the right field gap. It's all about how you place your shots!
Fouls are usually easy to see; however, there are times when they're not so clear.
A foul tip is always a strike, and unlike a foul ball, it can result in a strike three. A live ball is a foul tip. Runners advance (steal) at their own risk. If the catcher fails to catch the ball, it is a foul ball (dead ball). Runners stay put.
A foul-tip is a lawfully caught hit ball that travels sharply and directly from the bat to the catchers' hands. If it's a strike one or two, runners can steal or advance since the ball is still in play, and it's not a foul. It's a strikeout if it's strike three. If a foul tip isn't caught, it's just a foul ball. There are six fives per game and one of them must be thrown home.
The base on which the batter is standing when he hits the ball is known as his foot. If he steps off this foot before contact, the ball is illegal and automatic strikes are called. However, if the batter leaves his foot after making contact with the ball but before it reaches the catcher, then it is legal and the umpire should call it a ball. Even if the batter does not leave his foot, if he is distracted for some reason while batting, the ball is dead and the umpire has the right to call it a ball.
In any case, once the ball is out of the player's hand and beyond their reach, it's too late to steal. A thief can be awarded a run if the pitcher throws an error but that's about it. If a player is visibly annoyed with the fact that he or she was robbed of a base, they have the right to protest to an umpire. However, this should not be done frivolously since it can result in penalties such as time outs and ejections. In the end, the decision is up to the manager.
The catcher must catch a foul tip. A live ball is a foul tip. If a tipped ball strikes the glove but is dropped, it is considered a foul ball and the game is over. It's true. I developed a feel for the game 20 years ago, my first year as an umpire, after learning the rules and how to apply them. The hitter swings and tips the ball, which results in a strike.
Any foul bunt attempt with two strikes will result in a strikeout. When there are two strikes, any foul tip caught by the catcher results in a strikeout. A ball that is fouled and caught by a fielder is a foul out in any count. In essence, the regulation exists to encourage more and greater competition in the sport.
The runner might be thrown out by the catcher, or the runner could steal second. Either option is viable. The ball is still in play. It's the same situation as before, only this time the batter tips the ball, which strikes the catcher but he fails to catch it.