Two things can cause your problem, loss of subject focus points due to fast moving subjects and/or shutter speed to slow. Set the Autofocus Mode to AF-C. That way the camera will continue to focus on a moving subject, like in a basketball game. Now set the focus point on dynamic-area, AF. With the dynamic-area the camera will hold the focus even if the subject momentarily moves out of the focus area. These settings will help maintain subject focus even with fast action. Also as PavementPilot says to get stop action you need you need a high shutter speed. Shoot in shutter priority with a shutter speed of 1/500 sec. In the menu turn on Auto ISO with a high limit of 2500. Set the ISO in the control panel (press the ISO button) to 1800. (This will allow the camera to select the needed ISO between 1800 and 2500.) The camera will select the f/stop needed for a normal exposure. With the auto ISO turned on the camera will select a higher ISO setting, up to 2500, if it needs it for the exposure. The D7000 should give you good low grain shots even if the camera has to go to the 2500 ISO level. If you need an extra f/stop for your exposures change the shutter speed to 1/250 sec. I've always had good stop action using 1/250 sec., but 1/500 sec. works better. Hope this helps.