Between World Wars One and Two, when baseball dominated the nation's sport consciousness as the National Pastime, umpiring became a career vocation instead of a limited occupational opportunity. Expanded schedules meant seven months of employment, and umpires received better salaries and more recognition. Staff stability became the norm: an umpire who passed muster the first two or three years could look forward to a long career. Umpires continued to be vexed by arguments with players, insults from fans, and occasional flying objects, but the vicious rowdiness declined. The physical abuse was curtailed significantly because of the stiff penalties imposed for fighting and bottle tossing, while the verbal abuse abated as league officials and the press did an about-face after the infamous Black Sox Scandal by proclaiming the umpire the personification of the game's integrity. To underscore their role as independent arbitrators, umpires had to make travel arrangements separate from players and patronize different bars, hotels, and restaurants.

Umpiring had become a desirable and respectable vocation, but the odds against a major league career were far greater for umpires than for players. Competition was keen, as normally only one or two of the some two dozen umpiring positions came open each year. And the low pay, primitive working conditions, wearisome travel, and vicious abuse from players and fans that characterized the life of the minor league umpire drove out those who would or could pursue other employment. Moreover, there was no prescribed system of career development. Becoming a professional umpire was a matter of chance opportunity or personal contacts; there was no systematic evaluation or supervision of minor league arbiters; and advancement, even to the major leagues, was sometimes more a matter of politics and personalities than merit or ability. Nonetheless, those who persevered as "men of the cloth" and proved their mettle in the big time enjoyed a secure and esteemed career. Where Tim Hurst justified working as an umpire by saying, "You can't beat the hours," Bill Klem would declare, "Baseball to me is not a game; it is a religion."

Still, major league umpires received far greater recognition than remuneration. The pay scales for umpires were the same in both leagues. In the early 1900s the annual salary for major league umpires ranged from $1,500 to $2,000; by 1910 the top salary in the National League was $3,000, with only four of the seven umpires earning more than $2,000. Umpires who worked the World Series received $400 until Bill Klem demanded and received $650 in 1917; the next year Klem received $1,000 for the Fall Classic, but the pay for all other umpires remained $650. In 1937 salaries ranged from $4,000 for new umpires to $10,000 for the most veteran arbiters; umpires could expect an extra $2,500 from the World Series. Five years later the pay scale rose to $5,000 and $12,000, but compensation for the Series remained the same. Although the salaries for men at the top of the pay scale seem good for a l54-game, seven-month season, umpires had to pay all their expenses except railroad fares while on the road until 1940, when they received a $750 allowance for travel, a sum that most umpires argued covered only about one-half of their expenses. Moreover, they had to buy and maintain their own clothing and equipment, including ball-strike indicators, masks, and chest protectors. Nonetheless, better pay, working conditions, and status translated into more attractive and thus longer careers; twenty years' service was not uncommon. Consequently, both major leagues established a pension plan for retired umpires, but they were restricted to those who had served more than fifteen years and limited to $100 per year with maximum lifetime benefits of $2,400.

The size of umpiring staffs was also increased. The two-umpire system was the norm during the 1920s, but it became common practice to assign one of the reserve umpires to critical games or series; by 1933 three umpires were assigned routinely to regular-season games. The four-man crew was instituted in 1952. In the World Series the two-man crew, one umpire from each league, was used until 1908, when a pair of two-man teams alternated games. In the third game of the 1909 Series, all four umpires were on the field at the same time, thus establishing the four-umpire tradition that continued through 1946; in 1947 an "alternate" umpire from each league was stationed along a foul line in the outfield, thus creating the current six-umpire crew. Four umpires worked the All-Star Game from 1933 to 1948; the following year it conformed to the World Series format in putting the alternates on the field.