The downswing is an aspect of the golf swing which is often misunderstood.
The muscle movements in the downswing are the exact opposite to the backswing. The
biggest mistake I see is that people start the downswing with their upper half.
The biggest reason for this is that quite simply the club is attached to the arms therefore
it is natural without prior knowledge to try and hit the ball by starting the downswing with the upper half.
The correct way to start the downswing is to move the left hip first before the upper half.
This ensures that the club approaches the ball on a flatter swing plane thus producing shots that are cleaner with more distance.
As mentioned the left hip will go first before the upper half through a combination of lateral
movement and turn. This ensures that the body continues to move through the ball whilst
squaring up the club face through turning. It is also important to note that on the way down,
the arms should stay fairly close to the body with the wrists remaining hinged until the moment of impact.
Key indicators of a downswing that leads with the upper half are large divots, slice shots and pull shots. This is mainly because the club is approaching on a steep angle causing an outside-in swing path. This basically means hitting toward ten o'clock on the way through instead of 12(which is neutral) or 1 o'clock (which
promotes a draw).
The opposite can happen also with the legs pushing too far forward early on the downswing. This causes the upper half to be stuck behind the ball which means also hitting behind the ball. It may also cause hook shots to the left or block shots to the right.
Ensure on the way down as mentioned earlier that the left hip does go first, followed closely by the upper half.
If you can achieve this, you will produce a swing that is physically easier, more powerful and consistent.