Golf sway and weight shift, face on

Sway is the hips sliding away from the target as the club goes back, instead of turning. The view measures the middle of the pelvis at the top against where it was at address, in centimetres scaled from the golfer's height, and positive means away from the target. The starting guide is no more than 5 cm.

It's a position at one moment, not the path: a golfer who sways and recovers before the top reads small. Step through the backswing on the video if the number and what you see disagree.

Coaches talk about weight moving to the lead side, but a camera can't see weight. What it can see is where the pelvis sits between the feet: 0% directly over the trail ankle, 100% over the lead ankle, and more than 100% if it moves past the lead foot. The view reads it at address, at the top, at impact and at the finish, with starting guides of 55% or more at impact and 75% or more at the finish.

The view compares the head's position at impact with address, positive toward the target. A head that drifts toward the target before impact is the common fault this catches; the starting guide is no more than 3 cm.

Face on also shows how far the shoulder line tilts from level (positive when the trail shoulder is lower) at address and at impact, and how far the spine leans from vertical at impact (positive when leaning away from the target). At the top, the lead elbow's angle shows how straight the lead arm is, with a starting guide of 160° or more.

Turn is the reading to treat most carefully. A camera facing the golfer can't see rotation directly, so the view estimates it from how much narrower the shoulders and hips look at the top than at address: a line that has turned looks cos(turn) as wide. Tilt and tracking noise add to that, which is why the report calls it an estimate.

1. Put the phone on a tripod square to the golfer's chest, at about hand height.
2. Keep both feet, the head and the top of the backswing in frame from address to the finish.
3. Film at 60 fps or more if the phone can.
4. Pick Golf — side view in the report, and check the swing points against the video.

Face on, the shoulders look wide next to the torso; if they look narrow, the view warns that the clip may have been filmed down the line. The face-on readings are newer than the down-the-line ones, so check each point on the video before leaning on a number.