ClientGroup is the group where the GameConnections are stored by default when they connect to the server; findClientByName works by looping through there. You can use the methods .getCount(), which returns the number of objects in the group, and .getObject(int Index), which returns the object at the specified index.
For example:
for(%i = 0; %i < ClientGroup.getCount(); %i++)
ClientGroup.getObject(%i).delete();
// Disconnects all clients from the server (no real use, just showing looping)
ClientGroup.getObject(getRandom(0,ClientGroup.getCount() - 1)).delete();
// Disconnects a random client from the server (same as above, just an example)
EDIT: If you're curious of other methods, just call .dump() for ClientGroup while hosting sometime.