My neighbors are away Im feeding a cat and its kittens,. it attacked me when I came to check on them! help?

My neighbors are away for a week. another neighbor and I are supposed to be feeding and changing the litter of a cat and its kittens. I went to check on them earlier today when the mother cat began hissing, I ignored it and started to leave when the cat attacked my leg and scratched me up pretty badly. Iv spent plenty of time with the cat and its kitten prior to the owners leaving so I am confused on why the sudden defensiveness. How can I fend of the mother cat while still caring for her?