bonus baby

noun

: a baseball player given a large bonus to sign a first professional contract

In one scene Miguel asks a teammate who is a multimillion-dollar bonus baby fresh out of Stanford what he would do if his baseball career were cut short.—

Melissa Segura, Sports Illustrated, 6 Apr. 2009

specifically : one who signed under special rules that were sporadically in effect between 1947 and 1965 requiring that such a player be immediately added to a team's major-league roster for a period of time (such as one or two years) before being assigned to the minor leagues

… it was June 25, 1953, and the Tigers were playing the Philadelphia Athletics at Connie Mack Stadium. Kaline was 18, a bonus baby straight out of high school. —

Jeff Seidel, The Pioneer (Big Rapids, Michigan), 2 July 2012