David,
Usually, the boss are helped by their principal professionals and they choose players that they want in their team. The teams change regularly, depending on the tournaments’ level. Usually a tournament is on 3 weeks so it’s not rare to play in a different team every month. The important matches are the weekend, and so the Thursday, we play what it’s called a practice (without goal) to make horses playing and the players being together. It helps to work on adjustments.
PH