The trigger_once entity allows you to trigger an event, but only once.

usage

The trigger_once entity allows an event to be triggered when the player passes through the trigger_once area (the trigger_once area is defined by the brush it is assigned to). The only thing you need to fill in for this entity is its Target field. The only other key worth modifying is the Delay key which causes the trigger to not activate its events for a specified number of seconds.

In Day of Defeat, this entity has been modified to trigger once during each round, rather than the very first time a map is run. This behaviour can be overridden.