Jay Haas' unique swing has served him extremely well over his PGA and Champions Tours careers. Let's take a closer look at how it works. Jay's coach Bill Harmon describes Jay as "swinger" of the club and not a "hitter". While there really is no benchmark for classifying a player's swing, I think that is a fair description. Jay's arm swing and hand action dominates his swing, while his body follows. Most instructors would categorize Tiger as a hitter, while Phil Mickelson is more of a swinger. As Jay begins his swing, his first move is to lift his arms and the club to the outside, while very little of anything else is happening. Jay has said that throughout his career he often tried to change this, but inevitably comes back to the move that he makes naturally. Great players often tinker, but know that some movements are too ingrained to fix. A more conventional swing would likely produce worse results.
After Jay's initial takeaway, he begins to turn his hips and shoulders as the club swings back to a fairly conventional top-of-the-backswing position. The backswing definitely has the look of a two-part action. ... First the "lifting of the arms," and second the "turning of the body." This is what happens in a good golf swing: most players just blend these two pieces together more than Jay does. Kenny Perry makes a similar move, only in a more exaggerated fashion
One thing I really like about Jay's swing is his footwork. In the video filmed down the line you can really get a good look at how well his feet and legs work. In the backswing, his left heel lifts slightly as his left knee breaks in and toward the ball. He then replants his heel as he starts his downswing, similar to that of Tom Watson or Jack Nicklaus. Jay's footwork reminds me of a well-choreographed dance step. This rising and replanting of his heel is undoubtedly important to his timing and rhythm. Notice that his heel replants in the same spot, or maybe even slightly closer to the target. Raising your heel in your backswing can be a great tool to help produce a bigger hip and shoulder turn, just take note of where it replants. If you let your heel "backup" and it replants closer to the ball, your contact will likely suffer.
Lastly, notice how Jay's left leg straightens as the club swings through impact. This comes from the unwinding of his hips and is definitely a power source. Even players who feel that they are simply swinging the club, still definitely use their bodied effectively. Tiger seems to feel that this movement is what caused some of his knee issues, and is working on minimizing it. Granted Jay "snaps" his left leg at a far slower speed than Tiger does, but it doesn't seem to be slowing him down anytime soon.