Due to bad weather or the encroachment of housing developements, large open areas for horseback riding are disappearing. Meaning that a large number of serious riders are being sqeezed into sharing arenas more often than desired.
Having an understanding of arena etiquette is not only the 'nice' thing to do, it is imperative for safety's sake that everyone at a barn practice the same set of rules when sharing the relatively small space afforded in an arena. No one wants to get hurt and no one wants to be the one blamed for causing a wreck.
There are no standards set in stone and each barn seems to develop its own ways of dealing with high traffic, oftentimes the rules are unwritten and variable.
When the rules are ambiguous, the unitiated will unknowingly breach them and cause some onsternation. However, let common sense prevail, get a conversation going with the existing riders and agree upon protocol that will work for those currently in the arena.