» January 8, 1898: National League president Nick Young says he will have the more experienced umpires such as Tom Lynch, Bob Emslie, and Hank O'Day stay behind the plate when he institutes the new 2-umpire system. Previously, the single umpire would move behind the pitcher only with men on base.
» May 13, 1901: Trailing 7-6 to the Giants, Brooklyn loads the bases with two outs in the 9th. Bill Dahlen singles but the Giants throw out the runner going from 1B to 2B for the 3rd out. Assuming they are ahead by two runs, New York takes the field, but umpire Hank O'Day signals that just one run scored before the out. The Brooklyn players surround the ump, "gesticulating and throwing their gloves on the ground to add force to their arguments," writes the New York Times. O'Day finally has enough and calls a 9-0 forfeit in favor of the Giants.
» July 8, 1901: An 8th-inning decision favoring the Brooklyn Superbas infuriates St. Louis fans. When the 7-5 Brooklyn win ends, they rush umpire Hank O'Day, who suffers a split lip before players and police can rescue him.
» October 3, 1905: The National Commission establishes the rules for a World Series and names Hank O'Day and John Sheridan (both NL umps) to umpire it.
» June 21, 1906: At the Polo Grounds, umpire Bob Emslie tosses John McGraw in the 4th inning, but his fellow ump Hank O'Day goes one better, banishing Joe McGinnity and first sacker Dan McGann in the 5th. Down 4-2, Christy Mathewson relieves for the Giants and shuts out the Pirates over the last four innings. The Giants load the bases in the 9th and Chappie McFarland relieves a tired Sam Leever. A single scores one and with two outs, Doc Marshall singles to score the winning run. Mathewson wins, 5-4.
» December 26, 1906: National League umpire Hank O'Day suggests that the batter's box be outlined with white rubber strips rather than chalk, making it impossible for hitters to obliterate the lines with their spikes.
» May 21, 1907:
Three Finger Brown and Christy Mathewson hook up in a pitching duel, with the Chicago ace emerging the winner, 3-2. Matty's batterymate Roger Bresnahan makes two errors to cause Mathewson to lose his 1st of the year. Mobbed at the Polo Grounds after the loss, umpires Hank O'Day and Bob Emslie require police protection. The crowd is egged on by John McGraw, who will be thrown out of games seven times this year. The next day AL ump Billy Evans needs a police escort after argumentative Hugh Jennings incites a riot. Jennings will be suspended.
» September 4, 1908: In a game, the significance of which will not be recognized for another three weeks, the Pirates and Cubs are tied 0-0 in the last of the 10th at Pittsburgh. With two outs and the bases loaded, Pittsburgh's Owen Wilson singles to CF, scoring Fred Clarke with the winning run. Warren Gill, on 1B, does not get to 2B but stops short, turns, and heads for the dugout, a common practice. The Cubs' Johnny Evers calls for the ball from Jimmy Slagle, touches 2B, and claims the run does not count as Gill has been forced. The lone umpire, Hank O'Day, has left the field. When queried, he rules that Clarke had already scored, so the run counts. The Cubs protest to league president Harry Pulliam, but are denied. This is the first time the Cubs try this tactic, but not the last.
» September 23, 1908: Giants P Christy Mathewson and Cubs P Three Finger Brown battle in the most controversial game ever played. The score is 1-1, with two outs in the last of the 9th. The Giants' Harry McCormick is on 3B, and Fred Merkle (19, and making his first start of the year, is subbing for the sore-legged veteran Fred Tenney), on 1B. Al Bridwell singles, scoring McCormick. Halfway to 2B, Merkle turns and heads for the clubhouse in CF. Johnny Evers secures a ball (Joe McGinnity swears he picked up the ball that was in play and threw it into the stands) and touches 2B as the crowd overruns the field. Umpire Hank O'Day at 1B claims he didn't see the play, but that evening he rules the run does not count, and the game ended with a tie score. (Years later, in an interview, Merkle will describe it this way: "When Bridwell shot that long single, I started across the grass for the clubhouse. Matty was near me. When Evers began shouting for the ball, he noticed something was wrong. Matty caught me by the arm and told me to wait a minute. We walked over toward 2B, and Matty spoke to [Bob] Emslie. ‘How about this, Bob, is there any trouble with the score of the play?' ‘It's all right,' said Emslie. ‘You've got the game. I don't see anything wrong with the play.' Matty then took me by the arm and we walked to the clubhouse confident that we had won the game.")
» September 24, 1908: Harry Pulliam upholds Hank O'Day's delayed decision and declares the game a tie, a decision nobody likes. The Cubs demand the game be forfeited to them as the crowd prevented play from continuing, although darkness would have soon ended it. Both teams appeal. Pulliam sees no inconsistency with the September 4th incident and claims he has merely upheld his umpire on a question of fact in each case. Meanwhile, the Giants beat the Cubs 5-4, after almost blowing a 5-0 lead. Hooks Wiltse is relieved by Christy Mathewson, and the official scorer awards the W to Matty. The L goes to Three Finger Brown, his first loss to Mathewson since June 13, 1905.
» April 20, 1912:
After hitting the game-winning home run in the 11th inning to beat the Reds, 5–4, Cubs OF Jimmy Sheckard forgets and heads for the clubhouse after touching 2B. Teammates yell to him to complete the circuit, which he does. The manager of the Reds is Hank O'Day, who was the umpire that day in 1908 when Fred Merkle failed to touch 2B.
» February 9, 1914: Veteran umpire Hank O'Day, who managed the Reds in 1912, signs to skipper the Cubs.
» August 8, 1915:
Hank O'Day, who managed the Cubs in 1914, returns to umpiring.
» December 12, 1927: The National League reports more than five million attendance for the league in 1927, a new high. Veteran umpire Hank O'Day is named "player and umpire scout" for the league.