Sure! You are possibly arcing slightly inside in the backstroke and then trying to redeliver the sweetspot back out to the exact back of the ball. This causes an in-to-out path. You should not give sweetspot impact that much priority, and instead should make sure impact is with a SQUARE face moving straight down the aim line not just impacting the back of the ball but moving thru this back spot and also thru the center of the ball (which is also the aim line of address). Any part of the putter face works, not just the sweetspot, but the piece of putter face that impacts the ball needs to move straight thru the center of the ball, with the face square to the at-address aim line.
You may also be "hurrying" the thru stroke after a slight arcing to the inside. The two arms suspended from the two shoulders like chains of a swing from the top bar have a self-correcting action if the rear chain goes inside a bit, but this works best by allowing the two chains to DROP AND SWING -- then gravity realigns the rear chain under the shoulder line and the two chains / arms then swing straight. "Hurrying" this thru swing overpowers the corrective gravity "drop and swing" and CASTS the arms and putter in-to-out.
Finally, it is possible you are relenting a bit in the pressure on the front hand's thumb print on the putter handle. A too-loose grip allows the back-and-thru physics to open the putter face, and any lifting of the neck before impact plus inadequate grip pressure allows the putter COG rear of the face to drop around the hosel, which opens the face. Even though you say you have good grip pressure, still check this.
All together, feature square and online impact, steady thumb pressure, and no hurrying if the thru strike. Might get rid of the problem ...
An exercise is to set up facing a wall with the toe end close to the baseboard and make THRU strokes square down the line. Toe doesn't hit wall and face doesn't open.
The above is a negative -- don't hit the wall with an in-to-out path and don't let the face twist open thru impact. Here's the POSITIVE: stroke square and straight at the "corner spot" that is down the line off the front foot's big toe. The aim line and the line the ball needs to roll down for start line passes off the front foot a certain distance out, and a line from the big toe that meets this aim line in a perpendicular "corner" defines the SPOT the ball MUST roll over if the stroke goes straight where the putter face was aimed. Any stroke that rolls the ball to miss this precise spot to the outside -- as with your stroke -- would improve by identifying this corner spot and positively determining to roll the ball over it.
The "corner spot" (a PuttingZone innovation) is usually 5-7" down the aim line of the square putter face and about 6-7" out from the big toe for most adult males. To see it, look down the aim line and see a perpendicular line out from the toe to the aim line, and isolated that spot on the grass.
This "corner spot" integrates three main aspects of the putt: 1) the aim line based upon the read; with 2) the consistent body positions at setup for the aim and stroke; with 3) the stroke motion of the aimed body. Ka-Ching!!!
Being aware of this "corner spot" allows you to be POSITIVE in squaring the face at it, in stroking the putter face straight on line at it, and in rolling the ball at and to and over it.
At address, being aware of this "corner spot", the golfer implicitly or explicitly experiences a couple of "practice-stroke movies" of the forth-coming motion that greatly help the commitment to a good straight stroke.
If you have a standard sheet of paper 8.5" x 11" and placed it on the ground aimed sideways in "landscape" mode, with each foot's big toe at one of the inner-edge corners 11" apart and the ball just past the outer edge midway between the far corners, and the putter face aimed behind the ball exactly down the far edge AT THE CORNER, that's the same "corner spot" that is available for reference out on the course.
So this sheet of paper allows becoming more skillful at seeing the corner and at being sure the face's square aim points at the corner as usual (else the setup is a little different from usual), and at prefiguring the stroke motion before pulling the trigger.
One thing that eventually becomes noticeable is that this "corner spot" "feels" closer in to the front foot than one might expect. That's because the "no feel" usual deal is a stroke that leaves the setup on a slightly diagonal line out of the chest and shoulders, which is a faint holdover of how children putt poorly. "Feeling" the stroke passing the sweetspot square and straight at and over this "corner spot" as a bit closer than expected usually is a good thing. It's not a dramatic difference, but missing this "corner spot" by the width of a single blade of grass to the outside misses a dead-straight 10-footer by half a cup to the outside of the aim line.
Striking the sweetspot square and straight at, to and over this "corner spot" is actually a matter of a short thru stroke of about 5-6" that all happens before the putter head gets outside the stance and width of the feet. So focus on this short thru stroke being performed 1) rhythmically for pace, and 2) accurately for line.
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