A tailing loop is when the top leg of the casting loop falls below the bottom leg. This causes the two legs to cross, which is a recipe for disaster. Tailing loops are a common fly casting problem, but it doesn't take too much work to get your casting back on track. The main causes of tailing loops are overpowering, the forward cast, using too short a casting stroke, or trying too hard to "punch" the final cast for more distance.