The following players were lost due to the 50%  Required Useage Rule for the 1981 season.
 
I will list the team loosing the players, the players names and  primary position, and the year the player returns in the rookie draft.  An asterick indicates players who never play again in SPB.
 
Anok Island
Doe Boyland, 1b *
 
Baltimore
Garry Hancock, of  (82)
 
Baroda
Joe Rudi, of/1b (82)
Willie Stargell, 1b (82)
Mark Corey, of *
 
Cedar Rapids
Larry Cox, c (82)
Bill Robinson, of/1b (82)
Jay Loviglio, 2b (82)
Mario Ramirez, ss (82)
Dan Duran, of *
Reggie Walton, of (82)
Bob Jones, of (83)
Roland Office, of (82)
Steve Braun, of (82)
Rusty Kuntz, of (82)
Mike Willis, p *
 
Dorsey
Larry Littleton, of *
 
Hawaii
Rick Auerbach, ss *
Rick Sofield, of *
 
Lafayette 
Del Unser, of (82)
 
Louisiana 
Dave Schmidt, c *
Joe Charboneau, of (82)
Max Venable, of (82)
 
Moose Jaw
Mike O'Berry, c (82)
Randy Bass, 1b (82)
Rufino Linares, of (82)
Jim Tracy, 1b *
Dave Edwards. of (82)
 
New York
Tim Hosley, c *
Reggie Smith, of (82)
Bob Tufts, p (82)
 
San Diego
Johnny Oates, c *
Bob Pate, of *
Doug Rau, p *
 
Shelby
Greg Johnstone, of *
Brian Asselstine, of *
Dave Geisel, p (82)
Gordie Pladson, p (82)
 
Wright Patt
George Vukovich, of (82)
Rick Matula, p *
Jeff Schneider, p *
 
That is the total list of all players lost during the 1981 season.  I will begin working on the overusage penalties soon.  It will take a while longer due to the fact that I will have to check each player against his allowed '81 usage found on the SPB IV webpage.
 
Best,
Gary