This may be opinion-based, but can anybody explain why "kicked ball", i.e. striking the ball with any part of the leg, is a violation in basketball? I've always thought it seemed like a fair play, not much different from striking the ball with your arms or hands. Kicked ball violation calls slow down the game, and at least in the NBA, adds an additional element of judgement as to whether the kicking was intentional or not, although it always seems to be called regardless.
Whenever the basketball is intentionally hit by the leg/foot, a violation will be called. If a player uses a foot to prevent the ball from going out of bounds, it is a violation. If a cross-over hits the leg of an opponent intentionally, it is a violation. So, if the ball is blocked or hit intentionally by the leg or foot a violation might be called, no matter if you are defensive or offensive.
Not sure why more ball players do not use this to an advantage...it is much like being a goalie on the basketball court.
For a foot / leg infraction to be whistled voluntary is the first requirement. To be a foot violation it is necessary that whoever touches the ball with his leg does so as a result of a voluntary gesture. For example, if I am standing or making a legal defensive move, and you hit my leg trying to make a ground pass, there is no violation.
Once the voluntariness of the gesture has been clarified, then the concept of "advantage" can also be applied, although on the foot violation it is quite rare. For example: you pass the ball, I touch it with my foot but the ball still reaches your teammate unmarked under the basket. There would be a violation, but there is no booing so as not to dare an advantage to those who committed it.