From the description you’ve given, I don’t think there is a specific word that describes this type of person. However, there are terms that can be used to describes the people and event for the situation your presenting. The people attending these events are called “Fans.” These are enthusiastic people who are there to enjoy the game and root for their favorite team. There are several terms that can be used to describe the event. “Pregame event”, “Pregame activities”, “Pregame festivities”, or “Pregame experience”. All these terms can be used to reference the time spent doing activities before the start of the game. Like socializing, drinking, rallying or participating in a type of function exclusively held at that event. Here is an example of how these terms can be used in combination with your question. Ex. “My friends and I went to the pregame event and had a fun time with all the other fans that were there.” Ex. “I arrived early for the pregame experience because I wanted to see my favorite soccer player warm up on the field before all the other fans arrived.”