Brief History of Left Side Connection
Left side connection was invented by Sam Byrd and later popularized by Jimmy Ballard. Byrd was a sensational golfer (25 tour wins) who also played pro baseball at one time. He was known as 'Babe Ruth's legs' as he often would serve as a pinch runner for Ruth. during his time spent with Ruth, he began to learn Ruth's trick for hitting the ball with power by putting a handkerchief under his lead arm.
Later on, Byrd used this idea for his own golf swing and then taught it to Ben Hogan and according to Byrd, it got rid of Hogan's hook. It was later popularized by Jimmy Ballard who was the most popular instructor in the world in the late 70's thru the mid 80's. Ballard used this method with players like Hal Sutton, Curtis Strange, Rocco Mediate, Jim Colbert and many others. The theory being is that if the golfer can keep that handkerchief under their lead armpit while swinging, it will allow the big muscles in the body to swing the club and hit the ball instead of using the arms and hands to swing the club and hit the ball. In fact, I believe that Left Side Connection is just a way for the golfer to learn how to pivot properly so they can use the pivot to power the golf club instead of using their arms and hands to power the golf club.
What's the Drill For Left Side Connection
Take a golf glove or a handkerchief or a nerf ball and stick it under your lead armpit (left armpit for righties). Stick it WAY up there. Now, go and grip your golf club and take your stance. You should now feel that the upper left arm is pressed up against your upper left chest right around or on the left nipple area.
You want to swing the club while keeping that glove/handkerchief/nerf ball under your lead armpit and don't let that fall out of your armpit until THE HALFWAY POINT OF THE FOLLOW THROUGH. Even more importantly, you want to keep that upper left arm pressed against your upper left chest until the halfway point of the follow through. You will not be able to make a proper follow through if you keep that lead arm connected for the entire swing to the finish. At the halfway point of the follow through, it's alright to start folding the lead arm and allowing that glove/handkerchief/nerb ball to fall out. Here's a video showing a golfer using the left side connection drill. You will see what appears to be a white glove fall out of the golfer's left arm at about the halfway point of the follow through.
Again, this is just a drill. I think it's VERY important to not worry so much about the glove/handkerchief/nerf ball falling out as it is to keep that upper left arm pressed against upper left chest.
That's very much what SliceFixer's 9-3 drill is about. It's about keeping the left side connection up until the halfway point of the follow through.
Pictures of Left Side Connection In Action
One of my favorite pictures is of this baseball player's swing at impact. As you can see, the left arm is still 'connected.'
But yes, just about every golfer on the PGA Tour is 'connected' as well.
Now, I believe that most pros on tour do NOT actively think about left side connection. But I do believe that their left side connection comes naturally because they have a good/great pivot action and those hands are not getting too fast and out in front of the zipper on the downswing.
Where Golfers Screw This Up
Most screw ups consist of losing the connection at some point. However, the first thing I would advise against is trying to keep both arms connected. Many amateurs will also try to keep their right elbow tucked in. This isn't the problem (usually).
As you take it back you should feel the pressure of the upper left arm go from pressing against the upper left chest to more towards the middle of the chest. You will often hear about people having their left arm across the chest on the backswing. That's what a correctly connected left side will create for the golfer.
On the way down, many golfers are so used to being so active with their arms and hands that the will start to slide the left arm downward. That also can lose the connection. At the top of the swing it's *usually* best to keep the upper left arm pressed up against the chest and to start thinking about pivoting your lower body.
The last part that usually screws up golfers is that they lose their connection at or just after impact. Remember, it has to stay connected up until the halfway point of the follow through. But many golfers when they are about to make contact with the ball get disconnected. Again, that's what SliceFixer's 9-3 drill helps with so much. It keeps the left arm properly connected until the halfway point of the follow through...or the 3 o'clock position of the golf swing.