Keep a consistent circle, don't collapse the radius
For consistent ball striking you need a consistent circle (swing arc). A common fault is breaking that circle on the backswing by letting the trail elbow bend inside too quickly, which loses the radius of the swing and makes it very hard to return the club to the ball consistently.
Channel: Danny Maude
Watch official source at 1:04Why this context matters
Danny's diagnosis of the shared fault he saw across his members' swings.