Which of the following is NOT one of the characteristics from the big 12 characteristics?

The characteristic that is often considered outside of the big 12 characteristics is the flexed knee position. In the context of the swing mechanics and body-swing connection, the other options—S-posture, reverse spine angle, and early extension—are well established components that describe specific physical alignments or movements that can influence a golfer's performance.

The S-posture refers to a specific alignment of the spine that creates a more athletic position at setup, which ultimately affects how a golfer rotates during the swing. The reverse spine angle is recognized as an alignment issue that can lead to inconsistencies in swing path and contact, often needing to be addressed for improved performance. Early extension, meanwhile, describes a movement pattern that can disrupt the swing's timing and sequence, leading to undesirable outcomes.

The flexed knee position, on the other hand, does not feature prominently as a standalone characteristic within the big 12. While knee flex is important for maintaining balance and stability in the golf swing, it does not encapsulate a specific alignment or movement pattern like the others listed. Thus, it stands apart from the more critical characteristics that directly affect the body's relationship to the swinging motion.