The Goal Tending

In basketball, goaltending is the violation of interfering with the ball when it is on its way to the basket and it is (a) in its downward flight, (b) entirely above the rim and has the possibility of entering the basket, and (c) not touching the rim. In both NCAA basketball and NBA basketball, goaltending is also called if the ball has already touched the backboard while it is above the rim in its flight, regardless of whether it is in upward or downward flight. Goaltending in this context defines by exclusion what is considered a legal block of a field goal. In high school and NCAA basketball, goaltending is also called when a player interferes with a free throw at any time in its flight towards the basket. If goaltending is called for interference with a field goal, the shooting team is awarded the points for the field goal as if it had been made. In high school and NCAA basketball, if goaltending is called on a free throw, the shooting team is awarded one point and a technical foul is called against the offending player.

Goaltending is commonly confused with the related violation of basket interference. Basket interference is like goaltending in that it involves interference with a field goal when it may still go through the basket; when the violation is made by the defending team, the shooting team is awarded points for the field goal as if it had been made.

Consequences
# Goaltending calls lead to different consequences for offensive and defensive players. When officials finger a defensive player for goaltending, the team on offense is awarded two points. A goaltending call on an offensive player leads to a loss of possession of the basketball.
History of the Rule
# Dr. James Naismith invited the game of basketball in 1891. He wrote 13 original rules for the game that governed fouls, out of bounds and the concept that later came to be known as goaltending, among other things. According to USA Basketball, a portion of Naismith's eighth rule states: "If the ball rests on the edges, and the opponent moves the basket, it shall count as a goal." A number of basketball organizations added further conditions to the rule as the game progressed.
American and National Basketball Association Rules
# According to the NBA rule book, a defensive player may not make contact with the ball once it has reached its highest point during a shot attempt. If the ball is on the rim or within an extended upward circle the rim creates and a player touches it, goaltending is the appropriate call. Once the ball hits the backboard above the rim it may not be touched by a player. When it touches the backboard below the rim, a player may not contact the ball while it is travels in an upward direction. In addition, a player may not put his hands through the rim, touch the net or the rim when grabbing for the basketball.
Offensive Goaltending
# A defensive player can commit the goaltending infraction for all the above reasons. An offensive player can be called for goaltending in the event the player touches the ball while it is on or above the rim.
International and FIBA rules
# Once the ball hits the rim anyone may touch or grab it. Unlike American basketball, the imaginary circle extending above the cylinder is not used, so a ball on the rim may be rebounded by any player.


Source: Wikipedia & eHow.com