A Bloody L anchor is an anchor fault in which some of the fly line or leader is positioned at approximately a right angle to the rest of the anchor. The name describes the shape the anchor makes on the water: one part of it leaves the rest at roughly a right angle.

It is a layout fault, not a knot. The name sounds like a knot, and that is the trap — the question is about the anchor, so the answer has to describe how the line lies, not how two lines are joined.

Read the shape before the forward cast. The anchor is the fly and the line or leader in contact with the water at the bottom of the D loop, and a Bloody L shows that the anchor did not lie down as one line. The 180-degree principle for anchored casts asks for the delivery cast, the D loop and the anchor to be closely aligned laterally with the target, so an anchor bent through a right angle is worth checking against that alignment.

In a lesson, point to the two arms on the water and name the shape before the student makes another cast.

Source

From the FFI Fly Casting Definitions (August 2025); terms follow the FFI Fly Casting Definitions (Bloody L Anchor).