The penalty area, also known as the 18-yard box, clearly defines where on the field a goalie may handle the ball. A goalkeeper can leave his box whenever he likes, but it always carries an element of risk. Few coaches, players or spectators feel comfortable when their goalie strays too far.
As soon as a goalie leaves his box, the FIFA Laws of the Game treat him as any other outfield player. According to Law 12, outside his own penalty area, the goalkeeper has the same restrictions on handling the ball as any other player. Therefore, he may not catch the ball or handle it in any way while outside the box. If he does handle the ball, he will have committed a foul, and the opposition will receive a free kick. If the goalie deliberately handles the ball outside the area and, in doing so, prevents an obvious goal scoring opportunity, the referee has little option but to show him a red card and send him off the field.
Goalkeepers normally come out of the box when there is no imminent threat from an opposing player. If, for example, a goalie wants to get more distance on a kick upfield, she may dribble the ball a few yards outside the box to extend the range of the kick. In pressure situations, however, a stranded goalie is a recipe for disaster. In such circumstances, her defensive teammates must get back in support. Typically, at least one defender will sprint towards the vacant goal in an attempt to cover the space left by the goalkeeper. This is obviously not ideal, as an outfield player cannot use her hands to save a shot on goal.
When a goalie comes out of the box, attacking opponents will often try to capitalize on the situation. If the goalie has the ball at his feet, an opponent can try to rush him in an attempt to force an error or steal the ball. If the goalie reacts slowly or panics, a goal scoring opportunity may arise. If an attacking player is in possession of the ball while the goalie is outside the box, there are two obvious options available. The attacker can lob the ball over the goalie towards the open goal. Alternatively, the attacker can dribble around the goalkeeper and into the space behind, creating an easy goal scoring opportunity.
When a team is trailing by one goal with just a minute or two left on the clock, the goalkeeper will sometimes join his teammates in a last-gasp attacking situation. This is normally a corner kick, where the goalie's height and agility is useful. Few goalkeepers actually score in these desperate situations, but their presence can create havoc in the opposition's defense. The obvious downside to such attacking forays is the completely open goal at the opposite end of the pitch. If the attacking move comes to nothing, the goalie must sprint back to his box as quickly as possible.