Today sport is often used as an energy release, so we are more likely to dream of a sports arena or football pitch rather than an ancient arena. Spiritually an arena suggests a ritualized form of combat and sometimes sacrifice, but can also suggest the need for space in which to expand or enjoy group activities. We are developing a new focus of attention or an area of conflict. This conflict may need to be brought out into the open for due consideration. Dreaming of being in an arena, either as a player or as a spectator, highlights the fact that we may need to make the decision to move into a specifically created environment, one which gives more room for self-expression and creativity or theatricality. You might like to look at the entries for Competition, Games and Rite/Ritual.