Here is another little concept from Walter Neale's classic 1964 QJE paper "The Peculiar Economics of Professional Sports". One of the peculiarities he discusses is the multi-firm plant (a reconsideration of the more familiar multi-plant firm).
The concept of "plant" in economic theory is a "place" where production takes place. If the "output" of firms in sports is competition, then the firm as a unit of analysis in economic theory is the league. In order to produce competition, we need not only a league but a space in which to play. So a football stadium, for example, is a required input to produce football competition, and since teams "work" in stadiums to produce competition, the stadium can be thought of as a plant.
But playing spaces by themselves do not produce competition. For that you need multiple teams. One team by itself cannot produce competition for consumption by fans. There needs to be multiple teams playing with common rules, playing schedules, and a championship format, all mutually-agreed upon by the teams in the league. To have this at lowest average cost, you need a league.
Near the end of his paper, Neale writes "(t)he plant of economic theory is the game, which requires three factors of production: namely, land, labor, and labor." The playing space is one plant, and "labor and labor", meaning two teams competing, is a second plant. He correctly notes that if the product is competition, the firm in economics cannot be a team. This is Neale's multi-plant firm.
In my mind, each team produces effort against the other team. I suppose it is reasonable to think of a team, widely defined to include the players, coaches, trainers, front office personnel, practice fields, etc. as a plant. It simplifies things.
Or does it?
Updated: I have edited the title and deleted a duplicated word.