• A. A concave fly leg that crosses the rod leg
• B. A non-concave fly leg that crosses the rod leg
• C. Any loop that travels slowly
• D. Any wide loop

Answer: B. A trailing loop crosses the rod leg with a fly leg that is not concave.

Both faults finish with the legs crossed; the shape of the fly leg is what separates them. In a tailing loop the fly leg is concave — not straight, dipping towards the rod leg — before it crosses. In a trailing loop it is not concave and crosses anyway.

That is why the options about speed and width are not identifiers. A slow loop describes how the cast is travelling; a wide loop describes how open the loop is. Neither says whether the fly leg crossed the rod leg, and neither is part of the definition.

The vocabulary earns its keep when you diagnose. When the legs cross, look at the fly leg’s shape before naming the fault: concave gives you a tailing loop, non-concave gives you a trailing loop. They are two different reports, and the correction starts from what the fly leg actually did.

Source

From the FFI Fly Casting Definitions (August 2025); terms follow the FFI Fly Casting Definitions; exam details are in the CI Study Guide (2025).