Lag is a horrible, awful thing that plagues BZFlag players around the world.
What is lag?
While playing BZFlag, each player's client (the BZFlag program) needs to communicate with a server, which in turn communicates with other players' clients. The amount of time it takes for packets of information to be relayed from your client to the server is "lag." You can check lag for all players by typing the command '/lagstats' while playing. Keep in mind that lagstats shows an approximation of the amount of time it takes for a network message to go back and forth from one player to the server and back again, not the amount of time it takes to go from one player to another player. For example, if you fire a shot, your client sends a message to the server, giving shot direction and speed. The server then relays this information to all the other clients.
Other lag-related problems are "missing packets" and "jitter". These can occur if there are more severe network problems which cause messages between players and the server to simply get lost, or to be delayed by inconsistent amounts of time. In an attempt to keep this explanation simple, these problems will not be covered here, other than to say that they compound the effects of lag to an even higher degree.
Lag affects what you see while playing BZFlag, especially if the delay is high. The most common effect seen is "shots going through other tanks." Many times you will hear players say "my shot went through you", or "why didn't you die." Many people have been accused of cheating due to the sometimes misunderstood affects of lag.
How to fix lag depends on what is causing it.
Slow Internet Connection
Lag can be caused by a slow internet connection, such as dial-up. In that case, find a server that is more allowing, or get a better connection.
Satellite internet is far too laggy for BZFlag. Sorry.
Make sure Windows is not running its automatic update in the background.
Don't download something and play BZFlag at the same time.
Other programs, such as other people playing an online game on your network, can cause lag.