Professional Nikon D-SLRs have an AF-On button on the back which can be used to activate the autofocus, rather than the shutter release button. Many sports photographers prefer this way of working because it separates the act of focusing from the act of shooting. It takes a little getting used to, but most fans of this method say that once you’ve got to grips with it, you won’t want to go back.
The D7200 doesn’t have an AF-On button, but you can configure the AE-L/AF-L button with this AF-On function using the Custom Setting menu f4.
If you do this, the shutter button will still activate the AF in the normal way, which isn’t how back button focusing fans like to work. To disable this you need Custom setting menu a4. By default this is set to Shutter/AF-On, which means that both buttons activate the autofocus – you need to change the setting to AF-On only.