Trajectory and Velocity of a Basketball
The graph of the trajectory of a basketball is always going to be a parabola (an upside down bowl shape) when it is launched up into the air, and this is due to the affects of gravity as well as the force put on the ball by the player.
http://dustbunny.physics.indiana.edu/~dzierba/hp221_2001/projects/proj_basket/proj_basket.html
The ball's velocity changes as it moves through the air, but the velocity of the first half of the path will match the last half of the path. So, in the above graph, the starting velocity would wind up being repeated at the end of the path of a basketball. Often this doesn't happen because the ball collides with either the backboard or another player interfering with its path. The halves matching can be better seen in a graph of a full path as in the picture below. Now if the ball met nothing but net, then this means that it was almost completely uninterrupted in its path with a slight interruption by the net and it would look similar to the graphic below.
http://www.ac.wwu.edu/%7Evawter/PhysicsNet/Topics/Vectors/ProjectilesMotion.html
There are 2 independent forces on the ball as it is projected into the air. First there is a force in the vertical direction (force of gravity), then there is the force in the horizontal direction (force of player launching the ball) (Projectile).
The Independance of the Vertical and Horizontal directions means that a projectile motion problem consists of two independent parts :
* Vertical motion at a constant downward acceleration, which is equal to a = - g = -9.80 m/s 2 .
* Horizontal motion at a constant horizontal speed, v x = constant (Projectile).
As shown on Projectile Motion web site, 
[click the QT icon for the Quick Time movie (program requirement: Quick Time)], the horizontal speed is constant and air friction is not considered in this example.
As Hanson said in Basketball, the best angle has been estimated to be 58 degrees from the horizontal to ensure a successful shot.
