Check whether the putter face opens into impact
A putter face that becomes more open as it approaches the ball is moving opposite to the instructor's preferred closure pattern. In the example, the face moved from 0.61 degrees open earlier in the stroke to 1.15 degrees open at impact instead of closing by about 2.5 degrees over the final three inches.
Channel: Club Champion
Watch official source at 8:20Why this context matters
The instructor is interpreting measured face-angle data from a putter fitting.