You can observe a lot just by watching.
-- Yogi Berra
The best possible forecasts would incorporate all of the information available: play-by-play data, pitch-f/x, minor league scouting reports, injuries histories and, hopefully someday, hit-f/x and field-f/x. We have a long way to go but, bit by bit, we're using more and more information in our forecasts and the early returns are promising. In the two years since we starting using pitcher's fastball velocities (a crude measure of "stuff"), our pitching projections have paced the field (see here and here).If you're interested in finding out a little more, here's Dash's presentation from the 2012 Saber Seminar.