Final answer:
The question seeks the historical winter season during which soccer teams' standard size was established, but the specific winter season is not provided. Soccer teams consisting of eleven players became the norm by the late 19th century, however, the question may be referring to more recent changes in the MLS, which cannot be dated with the given information.
Step-by-step explanation:
The question refers to the history of soccer and specifically to the standardization of team sizes during a particular winter season. As the question does not specify a year, it's not possible to provide a definitive answer. However, it's noteworthy that soccer as a sport has evolved over time, including changes to the rules like the number of players in a team. Originally, teams varied widely in size, but by the late 19th century, it became standard for teams to consist of eleven players. These changes in rules were formalized by institutions such as the Football Association in England.
In the context of the Major League Soccer (MLS) conferences mentioned, the question might be referring to a more recent event in the evolution of soccer in the United States. The MLS has been known to make changes to enhance the game and its structure, but without a specific year provided, the changes to the teams and players' standards cannot be precisely dated within the provided text.