You're changing flies and there it is: a neat little overhand knot in your tippet, tied by nobody. Anglers call it a wind knot, which is one of fishing's great acts of diplomacy — because on most days, the wind had nothing to do with it.
A wind knot is a tailing loop leaving evidence. And a tailing loop, despite happening in the air, starts on the ground — in your casting hand.
How the knot ties itself
During the cast, your loop is supposed to unroll in one clean plane: the top leg of line traveling over the bottom leg with daylight between them. In a tailing loop, that daylight disappears — the top leg dips and crosses the bottom leg, and for a moment your line and leader are literally passing through each other's space. Most of the time they miss. Sometimes the leader flips through a loop of itself, and gravity plus the landing snugs it into a perfect overhand knot.
So the knot isn't an event. It's a statistic — cast enough tailing loops and some percentage will tie themselves off. If you're finding a knot every few outings, your loops are crossing far more often than that; the knots are just the ones that got caught.
Worth taking seriously, too, because an overhand knot in tippet substantially weakens it right where a good fish will test it. The knot you ignore in the morning is the pop you hear in the afternoon.
Follow it upstream to the hand
The line follows the rod tip, and the rod tip follows your hand. When the casting hand travels one straight, narrow lane — straight back, straight through — the loop unrolls in one plane and can't cross itself. When the hand weaves side to side, the tip's path bends, and the line gets sent along a track that folds across its own — the body-side ingredient of tailing loops, and therefore of wind knots.
The weave usually has an accomplice: an elbow that flares wide of the body mid-stroke, pulling the hand off its rail. And it loves fatigue — lanes that start straight tend to widen late in a session as focus fades, which is why the knots so often show up in the last hour.
You can't see your own lane from inside the cast, and a side-on view hides it too. The read requires the facing view: phone on a tripod pointed at you, a few false-cast cycles. That's precisely the angle CoachVision's AI coach uses to read whether your hand holds one lane or wanders — film a clip after your next session and you'll know within a minute whether your "wind" knots have a body-side source.
The drill — One-Plane Wall
Give the hand a lane it can feel. Stand a hand's width from a wall or fence line and practice your casting stroke beside it — straight back, straight through, 10 minutes, with yarn or no line at all.
The wall does the coaching: weave inward and it's immediately, physically there. The session's rule is simple — if the wall was ever in danger, the cast was weaving. Groove the stroke until the wall becomes irrelevant, and you've built the exact straightness that keeps the loop's legs apart in the air.
Then enjoy the quietest fix in fly fishing: nothing dramatic changes, your casting just stops leaving knots behind. Check your tippet at the end of each outing — the week it comes back clean is the week your lane got straight.