Disagreements in life happen often. Much of the time they result in hurt feelings and holding onto grudges. Sometimes these disagreements even occur during a sporting event... I know, hard to believe. But most of the time both players think they are right. Without a referee, a disagreement in a pick-up basketball game can put a halt to everyone's fun.
The solution: just cave. In the eternal scheme of things it isn't important if your foot was on the three point line or not.