Swaying, or when the trail leg gets out of position, is something I see very often with amateur golfers.
According to Titleist Performance Institute (TPI), over 37% of golfers suffer from this swing issue.
It can cause such a variety of destructive shots including a loss of power, thins or fats and make it impossible to coil and store power on the backswing.
The trail leg should act as an anchor and a stable platform from which to initiate the downswing and transfer weight.
For me, the best drill I like golfers to work on is to put an alignment stick into the ground on the outside of your trail leg. It should run from the outside of your golf shoe all the way to the outside of the hip, as shown in the image above.
This will give you a much better understanding and awareness if you are swaying.