Note: I also refer to this stitch in some of my patterns as a modified single crochet.
How to complete a modified waistcoat Stitch (modified single crochet): The modified waistcoat stitch results in a dense, warm fabric, with moderate stretch and has an appearance similar to a knit stitch. The modified waistcoat stitch is almost identical to a basic single crochet, with some minor tweaks to technique and stitch placement. To complete the modified waistcoat stitch, only insert your hook through the right post arm on the right side of the fabric only (do not exit through the right and left post arms on the wrong side of the fabric). I find the technique of using the hook end to pull the right arm toward the right and then slipping the hook through to the opposite side of your work. The hook should exit on the opposite side directly under the front and back loops (it should not exit through the legs of the stitch on the opposite side as it would with a traditional waistcoat stitch). Yarn over and pull through drawing it up a tad higher than working height (this well make the next round easier to execute). Yarn over and pull through.
This stitch works well with patterns stitched in the round, with no turning between rounds.
Where the traditional waistcoat stitch appears a bit more similar to a knit stitch, the modified version is a bit more simple to execute (in my opinion) and results in a slightly more textured fabric.
Pictures are shown worked in the round, with no turning between rounds.