The matchmaking in Battlegrounds is based on the following logic:
- Once 6 players tagged the Battleground, they will be entering the battleground together.
- The player with the highest Combat Power will join the Blue Team
- The player with the second highest Combat Power will join the Red Team
- The player with the third highest Combat Power will join the Blue Team
- and so on for all 6 players.
Due to the discrepancy in level and/or combat power, it can happen that the teams are not perfectly balanced (which is impossible to do), but you will never have all the strongest players in one team.