Although my own personal interest is more in videogames and board games, since these are what I professionally design, I am fascinated by all forms of play, and professional sports interest me more as a psychological phenomena than they do as an activity to follow. Watching other people's commitment to their football, baseball and basketball teams fascinates me, as their behaviour in this regard is often far more compulsive than any videogame addict (perhaps with MMOs excluded). Fans watch their team play every week, with religious dedication. They become quite upset if they miss a match.
Watching from home, one can easily argue that the player's sense of connection to the match is that of a spectator (although the individual may feel they have an influence on the outcome - even, sometimes, if they are watching a recording, since our impressions of agency need not be rational). But from the stadium itself, the crowd is something more than a spectator. They can actually influence the outcome of the match.
The most obvious example is with crowd noise: in a game of American football, for instance, in which the play requires expert co-ordination between the players, which in turn requires accurate communication, the roaring din of the home team can put off the visiting players, potentially leading to an edge. Then of course there is the effect on the morale of either team - there is certainly a psychological advantage to hearing a stadium full of fans cheer you on, and a disadvantage to having them shout you down in disgust. The term "the twelfth man" has been used in both football and American football to indicate the extent of crowd influence in the game.
With this in mind, is it really reasonable to consider the crowd as mere spectators? Are they not something close to an extra player - a super-organism of fans acting as one collective extra player for their team? And if so, what does this tell us about the disposition of play?