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An upright golf swing refers to how a golfer is swinging the club head back away from the golf ball. Every golfer has an optimal swing plane, that is an optimal angle that the golf club head swings around them on. If the player swings the club head on this plane, then they will be able to strike consistent, accurate and long golf shots. If a golfer has an upright golf swing, this means that they are swinging the club head around them at a higher angle than their optimal angle.
Swing plane can be demonstrated by using an alignment pole. If you take your set up position and hold the golf club as though you are about to begin your swing, push an alignment pole into the ground so that it enters the ground in line with the club head and so that it replicates the shaft angle of the golf club. This line that the alignment pole creates is your swing plane. An upright golf swing would see the club head travelling around you above this line, on a higher angle.
If you do swing on an upright plane, then you are using your arms more than your shoulders during your swing. As such, you will not rotate your upper body as much as you could and therefore you will not generate as much power and club head speed as you potentially could. An upright golf swing results in shorter golf shots.
An upright golf swing sees the club head approach the golf ball from the far side of the target line, or the outside. The club head then strikes the golf ball and moves across the target line to the inside of it. Rather than the club head swinging along the target line towards the target, it cuts across it and makes it difficult to hit straight golf shots that fly at the target.
An upright swing also sees the club head approaching the golf ball at a very steep angle so that the club head will connect with the top and upper part of the golf ball, producing low, short topped golf shots.
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To hit a straight golf shot, the head of the club needs to be travelling directly along the target line towards the target, with the club face aiming at the target. An upright golf swing promotes an out to in swing path which sees the club head cut across the target rather than swinging directly down it and as such, the ball will not fly straight at the target.
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An upright golf swing would see you moving the club head around them above plane at a much steeper angle than is optimum. If the club head is swung around you under plane, then you actually have a flat golf swing where the club head moves around you at too low an angle.
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An upright golf swing sees the club head swinging around you on a steeper angle than is optimal. As a result of this, the club head will achieve a very high position at the top of the back swing, not a low position.