Don’t get Cocky
Your Wrist is what we’re talking about!
If you’re casting and you hear the noise of your line slapping the water behind you, it is often because your wrist is cocking too far back. As it relates to fly casting, the wrist versus arm equation is a difficult balance to master, let alone explain. Remember the arm is the engine, the wrist is the steering wheel. This pertains to aiming the cast, not powering the cast. Continuing the comparison to driving, if you let your wrist power your cast you will crash.
A few simple fixes to help capture the right feel are;
(a) Get a large rubber band, wrap it around your casting wrist, and then insert the rod butt inside that rubber band when you practice on the lawn. If you find that the rubber band is flexing too much, odds are you are breaking your wrist too far.
(b) If you are wearing a long sleeve shirt, tuck the reel butt inside your cuff.
This can really sharpen up and help you regain your stroke.