Ah, no your issue there is something else. The LoL lobby client cannot be game captured, it's not actually a game, it's a browser window. Try these steps:
To best capture League of Legends, create two scenes. In the first scene, add a Window Capture of the LoL launcher/lobby (Windows 7 users should make sure Aero is enabled.). In the second scene, add a Game Capture of the game itself (you may need to be in a game to add this for the first time). Then configure the Scene Switcher to automatically swap between them.