All 1938 Managers,  Here is the full list of players who did not reach the 50% usage level.  
I will list the by team, name, manager,  primary position and what season they appear in next, 
or if they are done I will mark them with an asterisk.

Borger Gassers (Baxter)
Herb Bremer, C (1939)

Detroit Titans (Meyering)
Wayne Ambler, 2B (1939)

Fairfax Atlantics (Peterson)
Johnny McCarthy, 1B (1939)
Ossie Bluege, 2B  (1939)

Montreal Golden Buddhas (Barkun)
Ken Jungels, P  (1940)

San Diego Glaziers (Lehman)
Bill Atwood, C  (1939)
Earl Browne, 1B *
Jim Reninger, P  (1939)
Bill Weir, P  (1939)

San Francisco Seals (Ungashick)
Jim Bucher, 2B (1944)

Schenectady Blue Sox (Rahn)
Johnny Riddle, C (1941)
Bill Cissell, 2B  *
Woody English, 3B  *
Boze Berger, SS  (1939)
Julio Bonetti, P (1940)
 
Job well done as many of these players do not have much of anything left, while just a 
few have some usable seasons left.

The following teams had no one who did not reach 50% this season:  Brooklyn Dodgers (Murphy), 
Brunnerville Bean Brewers (Brunner), Frankfort Frogs (Plunkitt), Louisville Colonels (Applegate), 
New Haven Whiffenpoofs (Williams), New York Mutuals (DeZarlo), and West Baden Sprudels (Ryan).