Too many players fool themselves into thinking they have played good defense (despite their man making a shot) because they got their hand within an inch or two of the ball when it was shot. But how close you come to the ball has nothing to do with how well you defended that shooter. The crucial consideration is what are you doing while the shooter is deciding whether or not to shoot.
If you are standing there passively or playing possum and waiting for the block as the shooter decides to go up for a shot, then you will have no effect on the shot unless you touch it. Coming two inches from the ball is the same as coming two feet (or eight feet) from it. If the shooter expects to get the shot off and he shoots it accordingly, with confidence, it has nothing to do with you. Coming close to the ball after it is released may fool you, but it won’t fool your coach. Your activity is too late.
If you want to have an influence on a shot, if you want to make a shot difficult, you have to get the shooter’s attention while he is deciding to shoot. It is when he is deciding that you need to get him thinking about you, thinking that you might get there to block it, that you might touch the ball at his chest, or you might crowd him and prevent a complete follow-through. If you get him thinking about you, there is a good chance he will hurry his
shot or not concentrate as well, and more often than not, he will miss. No player is so good a shooter that he simply makes whatever he can get off. All shooters are at their best when they know in advance
they are going to be able to get their shot off.
For this reason, a small man can often defend a taller outside shooter
better than a guy who is the shooter’s size. It is not a question of whether or not the little man can touch the shooter’s ball. Very possibly he cannot. But can the taller shooter get free to set himself and bring the ball off the floor the way he likes to? Many tall players would rather go against a guy their size, a guy they have confidence they can fake out, rather than have to worry about a smaller but quicker man who tends to get underfoot and break up their rhythm with quick jab fakes and fast hands dangerously near the shooter’s dribble.
The crucial point is to worry the shooter before he shoots, while he is deciding. Once he goes up, it is too late. A player is likely to complete the shooting motion with the confidence and concentration he began it with.
A good defender has to interrupt that rhythm and concentration by gaining that shooter’s attention with jab fakes, violent movements— whatever it takes to get the shooter’s attention on you and off the shot. You don’t need to touch a shooter’s ball to make him miss. You merely need to gain his attention. Confident shooters make high-percentage shots, while distracted shooters, even great ones, shoot poorly. Everyone knows that.
But what is your style of defense doing about it?
From Dick’s book Stuff
Welcome To Keys To The Gym 
Wow that’s really interesting! Great advice, I will certainly remember that next time I’m out on the floor.
Glad to hear it Kate, thank you for reading and for sharing!