if the lag is intentional, then ban, but, i play often with mobile broadband, cause im in army.
Ofcorse i say BEFORE we start game that im on mobile and in army atm, and if people fail to read, grasp and understand that it might be unstable time to time and lag a bit, its not intentional. Thus, start whining... not my fault.
So i find banning people because of lag, dubios, at best... IF he is an ass, and do it on purpose, or dont warn people he might lag in advance. The, i understand that somesort of diciplinary actions might be in order. Still, a ban is harsh thing, espesialy since he might not actualy broken any End use agrements.