Playing under a pseudonym

This term is pretty self-explanatory; the practice of playing under a pseudonym occurs when a player decides to register/play under a name which is not their own. This may include various mononyms, names of historical figures, or even mere in-jokes. Notable infamous examples of quizbowl pseudonyms include Basileus.

Players who use pseudonyms might do so for a number of reasons. They might think it's funny for a personal reason or, more rarely-- and perhaps more scandalously, might also be trying to hide their actual identity for more suspicious purposes...

Many players/coaches/etc. who oppose playing under pseudonyms don't like it because it can result in a lack of complete or even reliable summary of statistics for a player, as it is impossible to determine what the actual identity of a pseudonym-using player was based solely on their stats entry. Even if the team of the pseudonym-using player is known, it is still very hard to track their identity down. Thus, some consider it a hallmark of bad quizbowl.

Teams playing under 'pseudonyms'

The equivalent of playing under a pseudonym for teams can be done for numerous reasons, including that the team might not be officially sponsored by the school they ostensibly represent. Teams that have done this include Hotchkiss (who currently play as "Team Coldhug"), Millburn (who have played as "Team Low Mountains"), and Whitney (who have played under the name "Goldenrod"). Unlike individual players, usually, for a team to play under a 'pseudonym' is generally not considered bad quizbowl.

Playing under given name only

Playing under one's first name only (or first name plus last initial) doesn't count as a pseudonym because it essentially constitutes a failure to properly sign up with complete information, not a deliberate attempt to hide one's name for a specific personal reason.