If you are playing multiplayer games on the internet, you might experience connection problems related to NAT (Network Address Translation). NAT'ing usually means a computer is not directly connected to the internet, but shares a connection with several other computers on the same network. Typically some kind of Router is responsible for sharing the connection. Depending on how the Router is set up, you may or may not be able to play online games of SketchFighter.
SketchFighter should inform you about these kinds of problems by displaying a message about your Router set up when you try to host or join a game.
If your computer is behind a NAT, and you have access to your Router setup, you may be able to change it in order to get better performance for SketchFighter in online games. Try forwarding port 33333 to the machine you want to use for playing SketchFighter. See your router's manual for instructions on how to do this.