Professional golfers spend most of their lives working on their games. They take lessons from the best instructors and constantly monitor their swings during practice. Many amateur golfers have never had a golf lesson and don't spend much time trying to get better on the driving range. Understandably, there are some big differences between the swing of a professional golfer and an amateur.
Professional golfers make a full shoulder and keep their left arm straight during the swing. A full shoulder turn and a straight left arm enable professionals to hit the ball on the downswing with power. Amateur golfers commonly don't rotate their shoulders fully and make the mistake of bending their left arm during the backswing. A bent left arm position robs amateurs of leverage on the downswing. The lack of a full shoulder turn also causes amateurs to chop down on the ball.
Professional golfers swing the club down to impact on an inside path. This means the it approaches the ball from inside the target line, allowing the club to swing through impact at maximum speed. Amateur golfers commonly swing down from outside the target line. Because the club is outside the target line on the downswing, amateurs have to pull the club across their body at the last second just to hit the ball. This motion robs amateurs of swing speed and accuracy.
Amateur golfers typically strike the ball with the club shaft angled away from the target, which adds loft to the club. This position causes shorter hits and a higher-than-desired ball flight. Professional golfers reach impact with the club shaft angled toward the target. This position takes loft off the club, producing a more penetrating and longer ball flight.
The average amateur swings through impact with an open club face and doesn't allow the club to rotate over properly until well after impact. This typically causes a shot that sails to the right of the intended target. Professional golfers are very good at squaring the club face at impact and letting the club release past their hands. This "release" allows the toe of the club to rotate over the heel in the follow through, producing straight shots.