Sandy Koufax, Harmon Killebrew, Al Kaline, and Roberto Clemente were all bonus players who went on to be elected to the Baseball Hall of Fame

The bonus rule was a rule instituted by Major League Baseball in 1947 to prevent teams from assigning certain players to farm teams. The rule stipulated that when a major league team signed a player to a contract with a signing bonus in excess of $4,000, the team was required to keep that player on their 25-man active roster for two full seasons. Any team that failed to comply with the rule lost the rights to that player's contract, and the player was then exposed to the waiver wire. Once a player remained with the team for two full seasons, he could be assigned to a farm team without repercussions.^[1]

The rule went through several variations. It was rescinded in 1958 but re-established in 1962, after Major League Baseball expanded, with different and more relaxed stipulations than the original. It was finally abolished in 1965, when the Major League Baseball draft was initiated.^[1]

In the late 1930s and early 1940s, major league franchises found themselves bidding against one another for the services of young players. These engagements subsided when World War II broke out. When the war ended, the bidding wars resumed and resulted in skyrocketing signing bonuses. To counter this, in 1947, Major League Baseball implemented the bonus rule. The rule's purpose was to prevent the wealthiest teams from signing all of the best players and from stashing those players in their farm systems. Additionally, the bonus market was weakened as a result of inhibited competition. In return, this limited labor costs.^[1]

The legitimacy of the rule was challenged several times after it was initially implemented. In December 1950, the rule was rescinded.^[1] In 1952, a committee chaired by Branch Rickey revived the rule. It was this iteration of the rule that stated a team had to place the players who met the bonus rule criteria on the major league roster immediately. Furthermore, the player had to remain on the roster for two years from the signing date.^[1]

Although players were signed as a result of their potential, many of them were not able to succeed. In an extreme case, pitcher Tom Qualters was on the active roster of the Philadelphia Phillies for all of 1953 and 1954, but pitched only 1/3 of an inning in one game of the 1953 season, and did not get into a game at all in 1954. Qualters did not appear in his second major league game until 1957, and never recorded a victory as a big league pitcher.^[2]

The New York Yankees worked out a deal with the Kansas City Athletics in which the Athletics signed Clete Boyer to a contract. The Athletics used Boyer sparingly for the two years they had him. Then, just days after the first date at which the Athletics could send Boyer down to the minor leagues, they traded him to the Yankees as the player to be named later from a trade the previous winter. This trade did not sit well with the owners of the other American League teams. They claimed that the Yankees had used the Athletics to hold Boyer. However, the deal was allowed by the league.^[3]

Incidents like the Clete Boyer trade showed how the bonus rule could be circumvented. Rumor also spread that teams were ignoring the rule and bribing players. In 1958, both leagues voted to rescind the rule. In addition, they rescinded it retroactively. This eliminated the major league roster requirement for the players signed in 1957.^[1]

After the league added four new teams (the Angels and Senators, followed by the Colt .45s and Mets), the bonus rule was reintroduced in 1962. The difference between the new version of the rule and the previous one was that a player had to spend just one full season on the roster instead of two seasons. The rule was rescinded permanently in June 1965, after the introduction of the Major League Baseball draft.^[1]

Players signed under the bonus rule were referred to as "bonus players" or "bonus babies". These players often went straight to the major leagues and, due to bonus rule, were prevented from spending time and developing their talent in the minor leagues. As a result, the rule came under criticism because it often caused such a player to languish on a major league bench instead of gaining experience in the minors.^[4]

Under the original bonus rule – in force from 1946 to 1950, and again from 1953 to 1957 – fifty seven bonus players were signed by MLB teams. Four of those players went on to have Hall of Fame careers: Al Kaline, Harmon Killebrew, Sandy Koufax, Roberto Clemente.^[1]

Of the four, only Killebrew, a bonus baby for the Washington Senators, saw any minor league service time once his mandatory two-year period expired.^[5] Clemente was signed as a bonus player by the Brooklyn Dodgers who sent him to the minors to allow him to develop; however, he was subsequently drafted under the Rule 5 draft by the Pittsburgh Pirates after one of their scouts took note his raw skills.^[6] Kaline and Koufax, on the other hand, never played in the minor leagues.^[7][8]

Other notable stars who signed under the original bonus rule were Dick Groat, Clete Boyer, Lindy McDaniel, and Johnny Antonelli.^[1]

Under the 1962 rule, which had more relaxed requirements, notable bonus players included Hall of Fame pitcher Catfish Hunter and Hall of Fame manager Tony La Russa.^[1] Hunter did not see any minor league service but did pitch in the Florida Instructional League before his major league debut.^[9]

• List of baseball players who went directly to Major League Baseball

• MLB Bonus Babies at Baseball Almanac