Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What was the minimum points against if the opponent is Port Adelaide?

### Inputs:
table_name: table, columns: ['Opponent', 'Played', 'Won', 'Lost', 'Drew', 'Premiership points', 'Points for', 'Points against', 'Percentage (%)']

### Response:
SELECT MIN Points against FROM table WHERE Opponent = Port Adelaide