The roll cast is a very efficient and effective cast and one you should absolutely know if you plan on fishing on creeks or streams. The primary purpose of the roll cast is to give you the ability to cast when a backcast is not possible. This may occur, for instance, if there are trees or bushes on either side or behind you. The roll cast is also effective when there is a stiff wind at your back or need to just quickly reset your fly.
The roll cast has evolved with the advent of the graphite rod. With older rods, like those made of fiberglass, it was more difficult to effectively load the rod. The roll cast was performed by raising the rod to a position slightly behind your ear and then quickly lowering the rod in the direction of the cast. Some describe the motion to that of “chopping a log.” A loop was formed and the line would feed out in front of you.
The graphite rod has made the roll cast fairly simple. With the line tight in front of you, lift the rod up to the one o’clock position (slightly behind your head). Then simply do a hard forward cast like you would do with an overhead cast. That’s it. The rod should load sufficiently to cast your fly in the direction you need. Don’t pause at the top position or the line will just pool in front of you.
What makes the roll cast work is the water surface tension on the line. This tension holds the line allowing you to load the rod during the forward cast. So, you will need to be near water to practice the roll cast.