Debut Games
In the biographical section of Baseball Reference player pages, there is a Debut section that notes the date of the player's first appearance in the major leagues, their age at the time, their stats in the game, and what their debut number is in major league history.
Clicking the date in that section will take you to the box score of the player's debut game, while clicking on "Debut" will link you to the list of all players to make their major league debut that year:
For Negro League players who later played in the American League or National League, the debut listed is for their first appearance in the major Negro Leagues, with the date and statistics for their AL/NL debut shown underneath. At this time, we do not have box scores for the Negro Leagues, so just the year of debut is shown.
Players to debut on the same day will have the same debut number - no consideration is made for the precise time of the day the player entered the game.
Debut Number Updates
While it might be expected that these debut numbers would remain the same, ongoing historical research means that these numbers are subject to change. For example, continuing research into the Negro Leagues has resulted in new players being discovered, some player being removed, and in some cases two records thought to belong to separate people have since been identified as the same player. There are more details on this from our 2026 blog post on Negro League updates here:
The SABR Biographical Research Committee have also discovered "new" players in major league history thanks to their ongoing research. Here is one such example of a new player from 1872:
Updates such as these will then cause debut numbers to change on the site.
Debut Game Quirks
There are some players who made their major league debut and later played in the resumption of a suspended game that started before the date of their debut. For example, Juan Soto made his major league debut on May 20, 2018. On June 18, he played in resumption of a game that had been suspended on May 15 - five days before his debut. In Soto's game logs the stats for that game will show up under May 15, but his debut information reflects that his true debut was on May 20.
Barry Bonds is another notable player who also appeared in the resumption of a suspended game that began before their debut.
Greg Maddux's debut game is listed as September 2 because his debut game began on that day. However the game was suspended, and Maddux did not actually appear in the game until the next day. A note is included in his Debut section clarifying this.
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