From Wiki Gonzalez
VORP stands for Value Over Replacement Player, a Baseball Prospectus statistic that measures "the number of runs contributed beyond what a replacement-level player would contribute if given the same percentage of team plate appearances."
Note that, while VORP is an adjusted statistic, it is a counting stat and not a rate stat.
In the past Baseball Prospectus set replacement level for VORP at:
- 70 points of OPS below league positional average for position players
- 1 RA above league average RA for pitchers
More recently they've moved to VORP replacement level at:
- 80% of the average offensive rate (85% is used for catchers, 75% is used for 1B/DH) for position players
- 1.37 * League RA - 0.66 for starting pitchers
- 1.70 * League RA - 2.27 for relief pitchers