This video will help you to block/kick devices connected over Wi-Fi.
Requirements : Android Smartphone , Root access enabled
Installation : Arcai's NetCut , which is available on Play store.
After installation of the app, open it, it will download some of its components and will self-enable its services. Meanwhile, You'll be able to see all the devices connected on your wifi network. Now, Tap on a specific device name which you think is unknown or which you want to discontinue from using your internet connection and that's it , you will see the red indications which means that the device is now temporarily terminated from using your Wi-Fi network , tapping back again will unblock it.
Note : This app is for Official or residental use. Do not try this on Public internet connections.