Your front foot has touched down and it is now time to launch. This is where you will uncoil all of the energy and power that has been stored up to this point.
Your hips will lead your hands. But what causes the hips to fire? The back knee will pinch forward and down toward the inside ankle of the front foot. The knee pinch launches the back hip and launches your momentum toward the baseball. It also helps prevent rising up on the back leg.
Before the hands commit to actually bringing the bat through the zone, they must line themselves up on the same plane as the incoming pitch. Use the bottom hand to drive the knob of the bat along the plane of the pitch. This guides the barrel and keeps it in the hitting zone longer.
Your back elbow should be in the slot close to your body. As always, your head is steady and you are locked on to the baseball.
Here is Mike Trout launching.