With the 1903 peace agreement between the National League and the new American League, major league baseball entered the modern era and brought stature and stability for umpires. Byron Bancroft "Ban" Johnson, president of the upstart American League, led in providing the strong support from league officials that was essential to the morale and effectiveness of the umpires. Noted for his backing of umpires when he had been the head of the Western League, Johnson insisted that umpires be respected and backed up his words by supporting their decisions and suspending players who were guilty of flagrant misconduct. In turn, he insisted upon tactfulness in contrast to the combativeness of the previous era. The National League followed suit, especially under ex-umps Lynch and Heydler, and by World War One, major league umpires enjoyed "unprecedented authority, dignity, and security." As umpire, manager, and baseball executive, Clarence "Pants" Rowland later remarked: "All umpires ought to tip their hats whenever Ban Johnson's name is mentioned."

Johnson also took the lead in dealing with the obvious handicaps presented by the single-umpire system. The game had long since become too fast and the players too devious for a lone arbiter to follow the action, let alone control the contest; moreover, in case of illness or injury clubs had to use a player to officiate the game. A three-umpire system, suggested in 1885 and actually used in the World Series that year, was an aberration, but a two-umpire system was much discussed in the 1880s and 1890s. Although the Players League of 1890 employed two umpires and in 1898 the two-umpire system was sanctioned in the rules, club owners continued to resist the expense of a second arbiter. After Johnson added a fifth umpire in 1902, the use of two arbiters became frequent, common, and then standard--an umpire-in-chief to call balls and strikes and a field umpire to make decisions on the bases. Again, the National League followed apace and in 1912 both leagues had ten-man staffs--two umpires per game and two replacements in reserve.

While front office support and the two-man system contributed greatly to the effectiveness of the umpire on the field, the enhanced stature of umpires was due perhaps as much to the personalities and contributions of the men who served in the first two decades of the twentieth century. That so many of the umpires who loom large in baseball history (and mythology) hail from the early decades of the century is partly the result of the extraordinary skill required to manage the game during the dead-ball era, when the bunt, stolen base, and hit-and-run were primary offensive tactics, and partly because of the media attention lavished on major league baseball at the time.

Ban Johnson, who personally selected his umpires with an exacting eye for ability and character, assembled an imposing staff for the American League. The senior umpire was John F. "Jack" Sheridan, veteran from the nineteenth century, who served as the acknowledged model for the younger men in both leagues and popularized working from a crouch position behind the plate. Another holdover was Franklin O'Loughlin, nicknamed "Silk" as a boy because of his long, curly hair, who successfully matched wits and words with players. College-educated William G. "Billy" Evans, who in 1906 became, at twenty-two, the youngest major league umpire in history, wrote nationally syndicated sports columns while working as an umpire, and went on to be a baseball executive. A fastidious dresser, Evans set the standard for the appearance of umpires on the field. English-born Thomas H. "Tommy" Connolly umpired the American League's first game in 1901 and thirty years later became the Junior Circuit's first umpire-in-chief (1931-54); patient and reserved yet firm, he established the league's tradition of ejecting players only as a last resort and once went ten years without a banishment.

The National League had its own illustrious arbiters. Outstanding were Canadian Bob Emslie, who for years umpired wearing a wig because his frazzled nerves caused premature baldness; hulking Cy Rigler, who while in the minors in 1905 started the tradition of raising his right hand on called strikes; Hank O'Day, stickler for technicalities, whose controversial Merkle decision in 1908 is a staple of baseball lore; and William J. "Lord" Byron, "The Singing Umpire," who periodically announced his decisions in melodious (if not poetical) singsong verse. But it was William G. "Bill" Klem, generally regarded as the greatest umpire in history, who dominated the league staff and set the style for Senior Circuit arbiters. Self-righteous and autocratic, Klem boasted of his scrupulous honesty and encyclopedic knowledge of the rules, intimidated players with threats of fines, and dramatically illustrated his insistence upon discipline and authority during arguments by drawing a mark in the dirt and warning antagonists, "Don't cross the line!" He also popularized the inside chest protector, the over-the-shoulder position for calling balls and strikes, emphatic arm signals for calls, and straddling the lines instead of standing in foul territory. Sharp-tongued and tough-minded, the highly publicized "Old Arbitrator," who vowed, "I never missed one [call] in my life," was for most of his thirty-six-year career the public's personification of the major league umpire. Upon retiring in 1941, Klem served as the league's first modern chief of umpires until his death in 1951.