The Keys to guarding screens are threefold:
One if you are the defensive man whose man is setting the screen you must give room for the defender being screened to get through the screen. We use to emphasize that the 'screenee' should always be the 3rd man through but as time has gone on we tell the man getting screened to 'not get screened', he can shoot the gap and get through or he can get on the hip and chase.
Second, if you are being screened make sure that you make yourself small by turning sideways and not allowing a full body blow to be set.
Third, if the offensive player is coming off the screen toward the basket, i.e. getting a backscreen, then man guarding the screen will have to protect the lane or the basket for one second while the man being screened gets through. The momentary switching might also occur if a man was receiving a down screened and subsequently curled the screen.
Finally, a defensive player might have to switch if he sees a man come off wide open. We'd prefer not to switch if possible.
