Sidearm casting has limited applications because it is inherently inaccurate and difficult to keep the backcast out of the fauna. It will, however, allow you to fish in windy situations that would collapse your overhead cast, and it is great for casting a fly under overhanging branches.

It also works wonders for tuning up your casting which is probably its greatest benefit. Using the sidearm cast, you can easily see the loops in both directions by just turning your head without moving the rest of your body. You can also easily see how the casting arc affects your loops because it all happens right there in front of you, in plain sight. You can also see just how much energy it takes to turn over a cast at different distances.

Here's how to do it. Stand at 90° to your target with your feet comfortably apart. Using the "thumb on top, extended finger grip", turn your hand palm up with your reel pointing to one side and your thumb pointing to the other. This is like a sideways karate chop with your thumb and the reel defining the plane within which you will move the rod. Now make your cast without twisting your shoulders. Viola! It works. It not only works, it works very well!

Work on your timing, paying particular attention to your backcast. Try to make the fly hover momentarily at the turn around point. That means you hit the timing perfectly. Then play with the casting arc to see the effect it has on the size of your loops. After practicing like this for 15 minutes or so, turn to face your target, use your normal overhead cast, and see what an improvement this has made in your casting. With a little bit of practice, casting under overhanging branches will lose some of its terror too!