Phase 3 is the heart of the swing and involves the rotation of the hitter’s hips, shoulders, arms, and wrists to accelerate the sweet spot of the bat through the hitting zone and hit the ball with as much force as possible. Phase 2, the Turn, was the rotational phase of the swing and was led by the rotation of the hips. Phase 3 is led by the hands - the key movement is to pull the hands through toward the pitcher while rotating the barrel out with the elbows and wrists.
Phase 3. Swing-to-Contact
3.1 KNOB FORWARD, BARREL BACK
From the Turn position (2.3), continue rotating the hip until your hands are out from behind your body and the knob of the bat is pointing directly at the ball and the barrel is pointing directly behind at the catcher. This knob forward, barrel back position is known as "bat lag" (not to be confused with bat drag which I discuss below) and every good swing should have bat lag.
Many swings in youth baseball go bad between positions 2.3 (Turn) and 3.1 (Knob forward, barrel back). It is one of the key transitions that I spend a lot of time on with my hitting students. Hitters instinctively know that they must get the barrel around to hit the ball, so the tendency is to start turning the wrists and elbows once they get into the Turn position and the hands stop moving forward, a mistake known as "casting". Turning the wrists and elbows too soon will cause your hands to move away from your body and result in an outside-in swing, where the barrel goes outside of the pitch then sweeps in across the hitting zone rather than directly up the hitting zone. The result is pulling every pitch, a lot of them foul; hitting a lot of pitches off the end of the bat; and an inability to hit an inside pitch. The bottom line is that after position 2.3 (Turn), the hitter must continue turning the hips until the hands come completely out from behind and into position 3.1, all without turning the wrists or elbows Once you've reached position 3.1, you can release the wrists and elbows; not before.
Another common mistake at this point in the swing is "bat drag", letting the
back elbow get ahead of the knob of the bat. Lead with the hands and knob
of the bat, not the elbow. Remember - bat lag is good, bat drag is not.
3.2 BARREL THROUGH THE HITTING ZONE
The Hitting Zone is the region where the barrel of the bat travels along the
path of the pitch. It's where the bat contacts the ball. The hitting zone
should run from about the middle of the plate to about 8 or so
inches in front of the plate, about 16-24 inches total. The center of the
hitting zone is roughly above the hitter's front knee. At 90 mph, the ball
passes through the hitting zone in 0.017 seconds (17 milliseconds). At 60 mph, it takes 0.025 second (25 milliseconds). With only a 17-25 millisecond margin for error, you can’t be sure where in the hitting zone your bat will contact the ball. So to give yourself the best chance of making solid contact, you want the sweet spot to travel up the full length of the hitting zone. Over the course of a season, that will translate into more hits.
From position 3.1, lock your front leg straight and complete your hip rotation, rolling your back foot onto the point, heel-high. Start to rotate your wrists to bring the sweet spot of the bat to the back end of the hitting zone. At the same time, start to extend the back arm forward toward the pitcher so the hands travel in a straight line parallel to the hitting zone, as shown on the photo sequence below. The movement of the back arm and the hand-path are critical. The extension of the back arm and hands forward toward the pitcher, rather than rotating them in front of your body, will keep the sweet spot in the hitting zone. If you don’t extend that back arm, the hands stop moving forward and the wrist rotation will carry the hands around in front of the hitter and pull the bat prematurely out of the hitting zone - a mistake known as “coming (or pulling) off the ball.”
3.3 EXTENSION OR THE "POWER V"
From contact (position 3.2), continue turning the wrists and extending your back arm until both arms are fully extend in an inverted V (the Power V) and the bat is pointing directly at the pitcher. In youth baseball or softball, few hitters get full extension into the Power V position. Getting into the Power V helps the hitter keep the bat in the hitting zone and hit through the ball, maximizing the force applied to the ball. As shown below, the swing phase can be thought of as whipping the bat from position 3.1, with the bat pointing straight behind the hitter, through the hitting zone to position 3.3, with the bat pointing straight ahead, with the hands moving on a line between those positions. It's the upper body (shoulders, arms, wrists) that does most of the acceleration of the barrel through the zone, which is why you should not use up those rotations prior to position 3.1.
The key positional checkpoints of the Full Extension or "Power V" position are:
On inside pitches, you can’t extend your arms into the Power V along the path of the pitch or you will hit the ball with the handle of the bat. Instead, you must let your elbow ride the hip a bit further in position 3.1 to pull your hands more in front of your body to get the barrel of the bat to the ball, then try to extend into the Power V out toward left-center field (right-center for lefties). It may be difficult to get full extension on inside pitches, and your hands may tend to follow a more circular path.