If you are using the special team trigger with the vault, you can't have teams switch between attacking and defending within the same level. Since each team cannot access the other team's base, the start positions at each team's base are sufficiently isolated, and so you can place the appropriate trigger zones around each of the start positions.

Please note that when the special team trigger is used and a client spawns for the first time in the level, the server still sends all of its triggers to client except the trigger ID belonging to the special team trigger is adjusted according to the team the client is on.