From the Hardball Times, with video:
Jefferies can get very pushy with his swing where it looks as if he pushes his hands out to the ball. Making matters worse, Jefferies looks to be working on this during his batting practice. Jefferies has a quick bat and keeps the bat head in the hitting zone for a very long time leading to a high contact rate, but it comes at the expense of a higher power output.
Tampa needs to work with him on letting the hands and hips turn together instead of pushing the hands out in front of the hip rotation. His swing is short enough to add a little length if needed. Jefferies could also increase his power output by continuing to fill out his frame.
Luckily for Jefferies, as a catcher, his bat will have much less pressure on it to succeed. He's more athletic than your typical catcher, but his arm is considered pretty fringy.