Who or what are the mudville 9 Casey at bat?

In Ernest Lawrence Thayer's poem "Casey at the Bat", the Mudville 9 represents the Mudville baseball team who are playing against an unnamed opposing team. The poem describes a baseball game between the Mudville team and an opposing team, with the Mudville team struggling to score. In the crucial moment, Casey steps up to bat for Mudville with the bases loaded, with the fate of the game resting on his shoulders. Despite the high expectations, Casey fails to hit the ball and is struck out, causing the Mudville team to lose. The Mudville 9 refers to the nine players on the Mudville team, including Casey.