remove_engaged_in_board_game_variables_effect

remove_engaged_in_board_game_variables_effect = {
	scope:bg_attacker = {
		if = {
			# Restrict to live characters to prevent errors.
			limit = { is_alive = yes }
			remove_variable = engaged_in_board_game
		}
	}
	scope:bg_defender = {
		if = {
			# Restrict to live characters to prevent errors.
			limit = { is_alive = yes }
			remove_variable = engaged_in_board_game
		}
	}
}

As written in game/common/scripted_effects/00_board_game_effects.txt.