Halfway back: the easiest frame to find

Two frames answer to the same name

P2, not P3Where the shaft-level backswing frame sits in the P-system

Two coaches asked for your halfway-back position can send you two different pictures. In the ten-point vocabulary that Jacob Watson of Golf Insider credits Mac O'Grady with popularising, the frame where the shaft first comes level with the ground is P2, the takeaway. HackMotion prints Halfway Back as the name of P3, and defines P3 as the moment the lead arm reaches parallel, which is later and higher.

This guide means the first of those: shaft level, hands still low. The collision matters, because your still and somebody else's are not comparable if they come from different moments. The level shaft's virtue is that everybody lands on the same frame. The Scientific Reports team evaluating low-cost video software used it twice as a phase boundary, acceleration beginning, in their words, from the horizontal club position.

Laid off, across the line, and the gap between

Both terms were coined for the top of the swing. HackMotion's definition of a laid-off club is the one in general use: the shaft points left of your intended target line rather than parallel to it. Borrowed backwards to the shaft-level frame, a shaft aimed left of the target line is laid off; one aimed right of it is across the line.

What sits between them is less settled than the diagrams suggest. Dr T. J. Tomasi of Keiser University College of Golf states one rule: when the club shaft is parallel to the ground it should also be parallel to the target line. Golf Distillery gives a different test for the same frame, checking in a mirror behind you that the butt end points directly at the ball. Those are not the same line, and the difference sits in the near-far direction one lens cannot see.

Why a phone copes well with this one

0 of 5Phases in that 2D-versus-Vicon club angle study that were this frame

Two things make this the kindest frame in the swing to a camera. The event is defined against level ground, and whatever else a video renders badly, it renders the horizon. Finding the top instead means finding a maximum, which those researchers define as the point where the club face is at its highest, and finding impact means finding a contact that at phone frame rates often falls between frames. Speed is the other. The club is nowhere near its quickest here, so the shaft draws a line rather than a smear, and the same authors had faster shutter speeds under trial to stop streaking spoiling the digitisation.

Finding a frame easily is not judging it easily. Young-Hoo Kwon and Chris Como, on the down-the-line view, note that perceived shaft alignment is substantially affected by camera position and by distance from the golfer, because the club's main motion runs at the lens. A moved tripod leaves the level-shaft test alone and ruins the shaft-against-the-target-line one. The validation everyone reaches for skips this frame: the Scientific Reports team named a mid-backswing in their own discussion as a moment when shaft angle alone interests coaches, then measured five others.

What a tidy shaft here does not buy

12-14 cmMale elite golfers' hands at address, measured off the club's working plane

The case for policing the frame rests on a chain: a club on plane here arrives on plane later. Three-dimensional data breaks the chain early. Kwon and Como tested whether the club returns at impact to the plane it started on. For most players it does not, and among the 200-plus elite players they had analysed the typical pattern is a club on a substantially steeper plane at impact than at setup.

They repeated the test without a lab, on frontal-view frames of Justin Thomas and Jason Day. In both, the club measured substantially longer in the picture at impact than at address; had it come back to its original plane it would have measured shorter. Their note also puts male elite golfers' hands at address 12 to 14 centimetres off the functional swing plane, the plane the clubhead works on through the ball.

Tidying the line your shaft draws going back does not hand you the plane it delivers on later. Watson's own verdict on the framework he had just finished explaining is the sentence worth keeping: forces move the golf ball, not positions.

What the frame is actually good for

Its value is as a fixed point of comparison. Because everybody lands on the same frame, it is the one backswing still worth sending to a coach, and the one worth holding a March lesson against in September. Filmed from the same spot each time, the shaft's direction there drifts when your takeaway drifts.

Compare it against your own earlier frames rather than a photograph of a tour player, whose height, club length and camera distance move the picture for reasons unrelated to a swing. Pebble Swing reads joint angles out of the frames and the backswing-to-downswing tempo ratio out of the motion, so this is a frame it can put a number on. The number describes where the club was, not what it does next.