Lazaro Antonio Díaz Sr. is an American umpire in Major League Baseball wearing number 63, a reference to his year of birth. He joined the American League's full-time staff in 1999, and has worked throughout both major leagues since 2000. Díaz was promoted to crew chief for the 2022 season, becoming the second full time Latino crew chief, after Alfonso Marquez.

In baseball, the umpire is the person charged with officiating the game, including beginning and ending the game, enforcing the rules of the game and the grounds, making judgment calls on plays, and handling the disciplinary actions. The term is often shortened to the colloquial form ump. They are also sometimes addressed as blue at lower levels due to the common color of the uniform worn by umpires. In professional baseball, the term blue is seldom used by players or managers, who instead call the umpire by name. Although games were often officiated by a sole umpire in the formative years of the sport, since the turn of the 20th century, officiating has been commonly divided among several umpires, who form the umpiring crew. The position is analogous to that of a referee in many other sports.