Dear Bastiaan,
When you say your stroke is inside-inside, I take that to mean either
1) that the shoulders move in a tilted plane, and this causes the putter to "appear" to move inside-inside when it is really rising on either side of the ball in a tilted plane, OR
2) that your forearms are rotating going back and coming thru while your path is going inside-inside in an arc OR
3) that your pivot at the base of your neck is describing a miniature arc in space that carries your whole torso's frontal plane in a swinging-door type action (even if your head seems to stay still). Any one of these actions produces what golfers commonly term an inside-inside path.
Regardless, in all three of these sorts of actions, ball position matters quite a lot, in comparison to the vertical-plane shoulder stroke with dead hands, and in slightly different ways. Taking the actions one by one:
1) Tilted-plane stroke with dead hands:
In this case, the rising of the putter on either side of the bottom of your stroke's crescent shape makes the putter "appear" to arc inside going back and inside going forward, but the putter is actually square to the putt line and square to the path at all times. The "path" is the crescent shape inside the tilted plane swept out in the air by the putter's sweet spot, and NOT the projection of this path in the air onto the ground.
Imagine that there is a coordinate system of three axes projected like a holograph at the ball at address, with the X axis being the putt line on the ground, the Y axis being from near to far thru the ball (perpendicular to the X axis on the ground), and the Z axis being straight up and down thru the ball. Planes are formed wherever two lines intersect (or where there is a line and a point off that line). The X-Z "plane" is the vertical plane that arises from the ground all along the3 line of the putt. Assume the ball is at the intersection of these three axes.
What makes ball position matter is the fact that the plane of the crescent path is tilted back towards you off the vertical X-Z plane. The putter face always impacts the ball with some "dynamic" loft resulting from the putter's designed-in loft plus ball position in relation to the rising or descending of the putter in its crescent-shaped path in the air (plus any weirdness of hands etc. in the stroke technique). But in a
vertical crescent path, this loft and this ball position issue doesn't matter much at all, because everything that results from it is directed in the vertical or X-Z plane, which is the same as the line of the putt (more properly, the "plane" of the putt, a vertical plane arising thru the putt line). You either hit the ball level, up, or down, but all impacts stay within this "putt plane."
There are two separate aspects to hitting the ball in a vertical-plane stroke, and neither matters much. The first is the actual loft, as described. And the second is whether the putter is ascending, moving level, or descending on its vertical crescent at the moment of impact, which is usually only due to ball position in relation to the stroke pattern (but may also include certain hand or other manipulations of the putter in the stroke).
In the vertical stroke action, where the crescent path is also vertical in the X-Z plane, more loft launches the ball into this plane, and so does playing the ball forward; negative loft or a descending blow pinches the ball into the somewhat spongy turf of the green, but this is also in the X-Z plane. There really is a nice range of ball positions for the vertical-plane stroke that extends from about 2 inches back from the bottom of the crescent path to as much as 5-6 inches ahead of the bottom. These variations cause losses of energy in the putt from launching, bouncing, or rebounding, as well as from some obliquity of impact, but in general there is not all that much adverse effect on ball direction.
However, when the stroke plane is tilted, thus tilting the crescent shape of the path in the air, the dynamic loft that results from putter loft plus ball position in relation to the stroke's tilted crescent path really matters. Imagine using a putter with zero loft and impacting the back of the ball right at the bottom of this tilted crescent path. the spot you really want to impact is the center of the ball, and this location is slightly forward of the exact bottom of the stroke. The precise moment the putter face makes contact with the back of the ball is the ONLY moment the putter face is square and moving square at the target. An instant after that, the putter face is following the tilted crescent shape rising into the air. Although the putter face stays square to the crescent shape inside the tilted plane, the putter face does NOT stay square to the X-Z "plane of the putt" and instead is headed inside in relation to this plane. Consequently, the putter's sweetspot does not really move straight and square thru the ball from the back dimple, thru the center of gravity at the core of the ball and on straight out the opposite front dimple. Instead, the putter face is closing during this time period of putter-ball contact, and the trajectory of the sweetspot of the putter thru the ball if from the back dimple on a crescent shape at a tilt thru the inside quadrant of the ball, missing the ball's sweetspot, and exiting at some inside-front dimple. That's cut spin, probably headed to the outside. And this is the BEST CASE SCENARIO unless you do something different with your path, the putter, or your hands.
When you factor in loft, the best case scenario gets worse. The loft exacerbates the tendency of the tilted-plane stroke to impart cut spin. And if the bottom of the actual crescent of your motion gets pushed a little out past the line of the putt, this impacts the ball from the outside back quadrant headed thru the center of the ball, and that is a dead pull.
When you also factor in ball position, you can correct for the loft of a perfect stroke in the tilted plane by playing the ball just a smidge back. it's sort of trial and error to find out where to play the ball until perfect tilted-plane strokes start sending the ball dead straight as aimed. Too far forward and the ball gets sliced and gets sent inside and is launched more than normal into the air. Too far back of the tilted crescent's bottom and the ball gets impacted inside-back quadrant outward, perhaps thru the ball's center, but with a little hook spin, and gets pinched into the dirt a bit, and starts to the outside.
Even once you have your ball position adjusted so that perfect tilted-plane strokes head straight away from the face as aimed, this approach falls apart if your stroke alters or if the ball position is not exactly the same all the time in your setup. The stroke "tilt" can easily alter, and even this change will change the way ball position affects the roll and direction of the putt. Not only do you have to always make the same stroke path along the crescent, but the crescent tilt also always needs to be the same. And obviously, if you change putter loft you have to start all over.
2) Forearms rotating in tilted-plane stroke (perhaps with a touch of armsiness separating from the "triangle" shoulder action going back and then thru)
This is essentially what Stan Utley teaches. This compounds the whole problem described above by further introducing the issue of timing the forearm rotation. I know how to teach the timing, but it's not a good idea to teach it, because it is a little too dependent upon "feelings" not connected to specifically directed movements of body parts. It's hard to learn, and harder to keep. Even so, the tendency is to be late in rotating closed into impact, so the ball is lost to the outside. Obviously, if the rotation closes too early, the ball is knocked inside by the closed face. So ball position matters just as much as in the tilted-plane dead hands stroke, but the technique makes performing consistently more difficult.
3) Pivot arcing and torso as a whole swinging like a gate
This is mostly a dead hands sort of stroke movement, but with the pivot arcing. When the pivot at the base of the neck remains still in space as a golfer swivels the shoulder frame back and forth on a stable axis, this is what happens in a vertical-plane stroke or a tilted-plane stroke. It's just the axis of rotation of the shoulder frame that differentiates the vertical stroke from all the possible tilted strokes, including a horizontal stroke. The axis is horizontal for the vertical stroke, and the shoulders move in a vertical plane that parallels the putt line. The axis is tilted somewhat for the tilted stroke, and the shoulders roatte in a plane that is perpendicular to the axis. In the horizontal stroke, the axis is vertical and the shoulders swivel completely in a horizontal plane. (But the axis of rotation is not necessarily or even best thought of as the spine, and is just the line perpendicular to the shoulder action.)
This particular stroke in which the pivot MOVES is similar to a top wobbling. In terms of a plane, if the plane of the torso from side to side (the "frontal" plane) is thought of as a sheet of rigid cardboard and the pivot at the base of the neck is a push-pin stuck in the center of the top edge of the card held at a tilt top forward, this action simple moves the push-pin in a miniature arc. This swivels the whole torso, but not about a stationary axis. Another illustration is to think of a cane, place your hand on top of the cane as the tip rests on the ground, tilt the top of the cane away from you a little, and then swing the top from side to side along an arc, like tap dancers do sometimes.
There's not a thing in the world wrong with this sort of stroke except that it is worse for pulling or pushing putts than the action of a tilted-plane stroke. If you impact the ball right on cue at the bottom of the stroke, it's no different. Compare this to the loft of the putter thru impact with this sort of wobble stroke when done with the axis starting out vertical at address. At the moment of impact, the putter loft sends the ball into the X-Z plane - no problem. But add back in the tilting of the cane / axis top out a little, and you reinject the cut spin.
David Lee teaches a putting technique that is close to a horizontal stroke path. he has found that this requires a special putter design and impact technique to make the ball consistently go straight away as intended. he describes the special putter design feature as similar to the toe-hook face of a hockey blade, and says this is needed to "trap" the ball thru impact. I believe this translates for an inside-inside stroke pattern with a normal putter into actually impacting the ball ever so slightly inside the exact back dimple of the ball. When you place a ball with its bottom dimple on a line of a putt, there is only one back dimple above that line on the ball's equator and only one front dimple above that line on the equator, and there are only two dimples in a line vertically above that putt line (bottom and top dimples). These two lines thru the ball intersect right at the ball's sweetspot in the center of the ball. By "trapping" the ball, I mean that the putter's sweetspot is moving from about one dimple inside the back dimple thru the ball's center at the first instant of impact, with the face pretty much square to the target. As the putter sweetspot follows the tilted crescent moving into and thru the ball, you would want the closing action to "trap" the ball before it heads outside the line and "throw" it straight down the line before the putter-ball contact is over. That's what is so bloody fragile about this technique -- getting that "trapping" action working with a precise tilt angle. Even this requires some fiddling with ball position to make it work.
In conclusion, ball position does matter for an inside-inside stroke path, mostly because of the tilted character of the trajectory of the sweetspot and the loft of the putter face. These aspects make ball position critical, but they also make the exactitude required in your stroke and setup from day to day and putt to putt much higher than necessary and tied to your ball position "fix" like a currency tied to the gold standard. Things can easily get out of kilter over time or under pressure.
Cheers!
Geoff Mangum
Putting Theorist and Instructor
Geoff Mangum's PuttingZone
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