How are you focusing? Do you know the back button focus/ AF-C technique? I stopped using the shutter button to focus years ago as I found it a much more reliable to be in continuous AF using the AF-ON button, using the shutter button only to trip the shutter. On a D7000 I don't think you have a dedicated AF-ON button, but you can configure the AE/AF lock button to act this way. For portraits using a fast lens wide open, that would be my choice of focusing.
What is this wizardry??