The reverse single crochet stitch (abbreviated reverse sc) is sometimes called the crab stitch. The actual mechanics of a reverse single crochet stitch are the same as for a regular single crochet — except in reverse.
Instead of working from right to left, you work from left to right. It creates a somewhat twisted, rounded edge that’s good for making a simple finished edge for your work. You usually don’t work stitches into the tops of the reverse single crochet, so you won’t find this stitch in the middle of a project.
Insert the hook, from front to back, in the next stitch to the right.

Be sure to have the right side of your work facing you.
Yarn over (yo) and draw the yarn through the stitch.

This step is similar to how you work a regular single crochet — only backwards.
Yarn over and draw the yarn through the 2 loops on the hook.

One reverse single crochet is complete.
Repeat the preceding steps in each stitch across the row.

This image shows several completed reverse single crochet stitches.
Take a look at the reverse single crochet stitch symbol.

Many people who crochet prefer to read crochet stitch diagrams instead of written instructions. This symbol for reverse single crochet stitch would appear in a stitch diagram.