One-Legged Swing refers to the first half of the High Level Pattern.

Power.

The problem is it ignores the just as important second piece.

Adjustability.

Logically, that leads to the creation of a swing that excels when it comes to Power but is deficient in terms of Average.

This has been driven home to me through my study of the swing of Albert Pujols.

Albert Pujols

Pujols started out with a Two-Legged Swing but, after leaving the Cardinals, became more of a One-Legged Hitter.

That explains why, while Pujols does still hit for Power, he no longer hits for Average.

One-Legged Swing

There are good aspects to the idea of a One-Legged Swing.

It's one way of describing Ted Williams' swing.

Ted Williams, advocated Rotational Hitting.

Rather than moving linearly, getting a big weight shift, staying closed, and leading with the hands, instead advocated a minimal stride and rotating into the pitch with the hips leading the hands.

Ted Williams

The idea was to power the swing with the large muscles of the core and legs rather than the small muscles of the arms, hands, and forearms.

However, and as Ted Williams admitted, the advent of the Slider changed everything for him; it made a One-Legged Swing no longer viable.