SELECT MIN("Points against") FROM table_27454 WHERE "Opponent" = 'Port Adelaide'
What was the minimum points against if the opponent is Port Adelaide?
CREATE TABLE table_27454 (
    "Opponent" text,
    "Played" real,
    "Won" real,
    "Lost" real,
    "Drew" real,
    "Premiership points" real,
    "Points for" real,
    "Points against" real,
    "Percentage (%)" text
)