The principle of Tilt states that, rather than keeping their
shoulders level during the swing, major league hitters vary the
tilt of their upper body out over the plate in order to hit pitches in different locations
(e.g. up and down in the strike zone) but still stay connected.
Tilt - Donnie Murphy
When thinking about tilt, remember that we are talking
about tilt out over the plate, not tilt back toward the catcher.
Every major league player must tilt out over the
plate to adjust to balls up and down in the strike zone.
However, different major league players will show different
amounts of tilt back toward the catcher.
Albert Pujols
For example, while Albert Pujols tilts out over the plate on
pretty much every pitch, his torso stays relatively upright and
he doesn't lean back toward the catcher.
Here are some more pictures of major league hitters tilting
out over the plate in order to adjust to pitches up and down in
the strike zone.