A woman player in white and black, sends the volleyball over the net, while the opposing team in navy blue, tries to block it, as the coach and a few spectators watch, in a gym.
They are in a gym
A player, an opposing team, a coach and spectators are group of people which can be shortened to "they".
The woman player, opposing team, coach, and few spectators are a "they."
They could refer to the woman player, the coach, and the few spectators.