The badminton net

Original fiction extract.

We had borrowed a net for the holiday club and set the posts at opposite sides of the lawn. The net sagged between them, its centre hanging well below the tops of the posts. My first shuttlecock crossed without rising above my head. The organiser checked the cord instead of telling me I had made a wonderful shot. Once the net was properly supported, we had to begin again. My younger sister said the earlier version had suited her better. She stayed to practise, though she did not forgive the cord immediately.

Use your own words to explain what the word “sagged” means in this extract.