A lot of people are unaware how people even with cable modems can create lag in (player hosted) games. If you are running bit torrent, kazaa, or some other file sharing program where you are constantly uploading and downloading, you will heavily tax your bandwidth. This means even if you have a cable modem you will lag heavily. It's a more common problem with people who use routers. So the next time you're in a Brawl game, and lag is present, consider this being the most common occurance.
Please turn OFF any file sharing programs while in a Brawl match, and if you must leave them on, set your upload rate to a very low value until the lag disappears.