Bresnahan was one of several players who became a close friend of John McGraw. With Christy Mathewson, another friend, it was an attraction of opposites. Roger could have been McGraw's twin: compact, pugnacious, fiercely concentrated on the game, and skilled in all the ways it takes to play it. Temperamental like his manager, he was an unabashed Irish brawler, tough on teammates who did less than their best, tough on opponents, toughest on umpires, whom he baited and bedeviled. He was frequently ejected, fined and suspended, gave headaches to League officials, and engaged in noisy confrontations with at least three club owners. He could play any position on the field.

Washington had him first as an 18-year-old pitcher who shut out the Browns, 3-0, on six hits in his major-league debut. His repertoire was dazzling. The papers credited him with "a speedy shoot, outcurve, inshoot, drop ball." Roger won three more games that season, but the Senators let him go the next spring when he insisted on more money than they would pay. The Cubs brought him up after two years in the high minors, played him for two innings, and lost him to McGraw's Orioles in 1901. Rapped hard in two outings, he was tried at second, third, the outfield, and when Wilbert Robinson was hurt, behind the plate. He played well wherever they put him, but catching was his forte. When McGraw departed the American League for the Giants at mid-year, Bresnahan made the leap with him. The Giants had Jack Warner and Frank Bowerman as their catchers, so Roger became the centerfielder. The season was a romp. Despite his hefty build, he was fast and agile enough not only to cover the outfield expanse, but to bat leadoff. He played 116 games, got 142 hits and batted a handsome .350, his career high and a mere .005 behind Honus Wagner.

By 1905 Bresnahan was the Giants' first-string catcher. Some say Mathewson urged McGraw to make the move, although Mac had known Roger's capabilities for years and could have figured it for himself, particularly now that he had acquired Turkey Mike Donlin for the outfield. Roger had another good year, hitting .302 and catching 87 games. He caught all five Series games against the Athletics, which meant Matty's three shutouts, Joe McGinnity's one, and Joe's shutout loss to Chief Bender. He also hit a sparkling .313.

Perhaps his most notable contributions to the game were in protective equipment. In 1905, after being hospitalized for a head injury from a beaning, he experimented with a batting helmet manufactured by the A.J. Reach Company. It was like the leather football helmet of the period sliced vertically: one half for covering the left side of a righthanded batter's head, the other for the lefty hitter. Although beanballs were frequent, the idea did not find favor. Two years later he devised catcher's shin guards. The first ones, evidently modeled after a cricketer's leg pads, were large and bulky, with a knee flap that came up to the thigh. They were greeted with ridicule and protest, but soon caught on. By 1909 they had more utilitarian shape and size, and were in general use. About 1908 he improved the flimsy wire catcher's mask with leather-bound rolls of padding to absorb the shock of foul-tips.

In winter that year, McGraw traded his friend to St. Louis. Roger had caught 139 games during the season, but he was 29 and slowing down. McGraw could afford to let him go. He had the young Chief Meyers on deck and the Cardinals eager to make a deal. Long a lackluster club and a cellar-dweller for two years, its owners thought a manager like the fiery Duke of Tralee might energize the players. To get him they gave up three of their few talents: Red Murray, a first-rate outfielder, Bugs Raymond, an eccentric but effective pitcher, and an experienced backup catcher, Admiral Schlei, acquired from Cincinnati.

Manager Bresnahan acquired some good players and got them above .500 and in fifth place by 1911. The Cardinals' owner, Mrs. Schuyler Britton, who had recently inherited the club on the death of her uncle, Stanley Robison, was pleased with the improvement and rewarded Roger with a five-year contract at $10,000 per year, plus a percentage of the profits, if any. During the disappointing sixth-place season of 1912, however, Mrs. Britton, like owners before and since, second-guessed her manager publicly. Roger blistered her ears with some choice dugout repartee and was fired forthwith. Roger demanded to be paid as manager and player for the remaining four years of his contract. The Cardinals, unable to clear waivers for a trade, finally sold him to the Cubs. He backstopped Jimmy Archer in 1913, managed Chicago to a fourth-place finish in 1915, all the while continuing his contract fight with the Cardinals. He finally won a $20,000 settlement. His playing career ended in 1916.

After leaving the major leagues he managed, and for a while he owned Toledo of the American Association. In 1921 he and Jim Thorpe were granted a National Football League franchise, but the team never got off the drawing board. He was owner-manager of his hometown Toledo Mud Hens through 1923, then coached McGraw's Giants (1925-28) and Tigers (1930- 31).

At the age of 64, Bresnahan once again donned the tools of ignorance and caught for Walter Johnson in an exhibition to raise money for war bonds. Bresnahan died in Toledo in 1944 and was elected to the Hall of Fame posthumously in 1945.