Basil does often have ruffled looking leaves so it could just be natural. But there might be some aphids sucking the sap from the foliage. I can't see any in the pictures but have a very close look under the leaves and around the growing tips for small, soft, oval bodied insects. If you're not sure Google aphid images.

I don't see any but I'm planning to take another look tomorrow with a magnifying glass. When I held the plant up to the light, I could definitely see some spots where the leaves looked almost bruised/damaged. I also just noticed that the main veins of the leaves look almost rust-brown in color. Could they be hiding in the dip of the veins?