“Merkle’s boner” occurred on September 23, 1908, when New York Giants baseball player Fred Merkle—running from first base in the ninth inning of a 1-1 game—saw the winning run score and ran off the field to celebrate victory, neglecting to touch second base. The game was re-played, the Giants lost, and the rival Chicago Cubs won the pennant. Although Merkle—then just a rookie player—went on to have a fine baseball career, he was always known for “Merkle’s boner.”
 
The term “bone head play” (or “bonehead play”) had existed from 1906 and 1907. The term “boner” (short for “bonehead play”) was used by 1909, and “Merkle’s boner” was called that by at least 1915.
   
   
Wikipedia: Fred Merkle
Frederick Charles Merkle (December 20, 1888 – March 2, 1956) was an American first baseman in Major League Baseball.
 
Career
Born in Watertown, Wisconsin, he played infield for 16 seasons in the major leagues with the New York Giants, Brooklyn Robins, and Chicago Cubs of the National League, and after playing in the International League from 1921 to 1925 he appeared in 8 games with the New York Yankees of the American League before retiring in 1926.
 
In 1910, he was 4th in the NL in doubles (35) and slugging percentage (.441).
 
In 1915, he was 6th in the NL in batting (.299).
 
Merkle’s boner
On Wednesday, September 23, 1908, while playing for the New York Giants in a game against the Chicago Cubs, while he was 19 years old (the youngest player in the NL), Merkle committed a base running error that later became known as the “Merkle Boner,” and earned Merkle the nickname of “Bonehead.”
 
In the bottom of the 9th inning, Merkle came to bat with two outs, and the score tied 1-1. At the time, Moose McCormick was on first base. Merkle singled and McCormick advanced to third base. Al Bridwell, the next batter, followed with a single of his own. McCormick advanced to home plate scoring the winning run for the game. The fans in attendance, under the impression that the game was over, ran onto the field to celebrate.
 
Meanwhile, Merkle, thinking the game was over, walked to the Giants’ clubhouse without touching second base. Cubs second baseman Johnny Evers noticed this, and after retrieving a ball and touching second base he appealed to umpire Hank O’Day to call Merkle out. Since Merkle had not touched the base, the umpire called him out on a force play, and McCormick’s run did not count.
 
The run was therefore nullified, the Giants’ victory erased, and the score of the game remained tied. Unfortunately, the thousands of fans on the field (as well as the growing darkness in the days before large electric light rigs made night games possible) prevented resumption of the game and the game was declared a tie. The Giants and the Cubs would end the season tied for first place and would have a rematch at the Polo Grounds, on October 8. The Cubs won this makeup game, 4-2, and thus the National League pennant.
 
Varying accounts
Accounts vary as to whether Evers actually retrieved the actual game ball or not. Some versions of the story have him running to the outfield to retrieve the correct ball. Other versions have it that he shouted for the ball, which was relayed to him from the Cubs’ dugout. And still other versions have it that Giants pitcher Joe McGinnity saw what was transpiring, and threw the actual game ball into the stands; thus the ball that was picked up by or relayed to Evers was a different ball entirely. The New York Times account of the play recalls that Cubs manager and first baseman Frank Chance was the one who “grasped the situation” and directed that the ball be thrown to him covering second base.
 
At the time, running off the field without touching the base was actually common, as the rule allowing a force play after a potential game-winning run was not well-known. However, Evers was noted as an avid studier of the official rules of the game, and ensured that the rule was known to everyone afterward.
 
Aftermath
Giants manager John McGraw was furious at the league office for robbing him of a victory (and a pennant), but he never blamed Merkle for his mistake.
 
(Historical Dictionary of American Slang)
bonehead play n. a foolish and obvious blunder
1911 A.H. Lewis Apaches of N.Y. 107: I don’t know as I’d call it a vice so much as a bonehead play.
1928 MacArthur War Bugs 104: Shelter halves wereoozing with mud, another result of the bonehead play.
1940 E. O’Neill Long Day’s Journey1: A very bonehead play!
1951 Bowers Mob (film): it sounds like a bonehead play, but the badge he flashed was the McCoy.
1957 Shulman Rally 194: She was much too smart for such a bonehead play.
 
(Oxford English Dictionary)
bone-head slang (orig. U.S.), a block-head; also attrib. or as adj.; bone-headed a. slang (orig. U.S.), thick-headed, stupid; hence bone-headedness.
1908 C. DRYDEN in Chicago Daily Trib. 24 Sept. 12/1 Then came the *bone-head finish which left the bugs puzzled and wondering.
1909 R. BEACH Silver Horde xx. 271 What’s the use?.. That bone-head wouldn’t understand!
1915 J. LONDON Let. 5 Nov. (1966) 463 Now, why be serious with this bone-head world?
1917 CONAN DOYLE His Last Bow viii. 292 James was a boneheadI give you that. 1958 J. & W. HAWKINS Death Watch (1959) iii. 82 The best of us have made a bonehead mistake or two.
 
1903 Smart Set IX. 96 You talk like a *bone-headed fool!
1915 WODEHOUSE Something Fresh v. 149 You blanked bone-headed boob!
1923 Adv. Sally xiii. 212 The wilful bone-headedness of our fellows.
 
(Historical Dictionary of American Slang)
boner n. BONEHEAD PLAY
1912 American Mag. (June) 200: Boner—a stupid play; a blunder in the science of the game.
1915-17 Lait Gus 178: he found out before he got back to Picadilly that he pulled a boner.
1918 Chi. Sun-Tribune (Mar. 24) II 1: A pair of boots and a boner let in the tying tallies.
1920 Ade Hand-Made Fables 119: before he had a Chance to pull a Boner and suggest the prehistoric Euchre, all the Card Tables were whisked away.
 
(Oxford English Dictionary)
boner
slang (orig. U.S.).
[f. BONE n. + -ER; cf. bone-head.] 
A mistake, a blunder.
1912 Amer. Mag. June 200/1 Bonera stupid play; a blunder in the science of the game.
1913 Ibid. Sept. 94/3 Got his signals mixed and pulled a boner.
1933 Passing Show 9 Dec. 9/3 Poor Carol… She made a boner to-night… Ronnie was simply livid.
1960 Spectator 7 Oct. 509 This Government has made about every boner possible. 
 
Chronicling America
2 September 1906, San Francisco (CA) Call, pg. 41, col. 5:
Three hits, coupled with Sweeney’s sacrifice and some bone-headed playing by Wilson, Irwin and Wheeler, who failed to catch two men between the bags, gave Portland three runs and the game.
 
8 June 1907, Sporting Life, pg. 7, col. 2:
Poor pitching, mediocre fielding and ineffective batting, combined with bone-head plays, made the Nationals a veritable laughing stock here.
 
3 August 1907, Sporting Life, pg. 4, col. 2:
Where, oh where, did that expression “bone-head” originate? Must have been in the minors.  Col. B. thinks so for two communications from small league men have contained the phrase.
   
Chronicling America
26 September 1907, San Francisco (CA) Call, pg. 10, col. 1:
Brashear flied to left and Smith made the prize bone head play of the day with a wide throw to second, when he could have come in and handed the ball.
 
5 October 1907, Sporting Life, pg. 15, col. 1
The locals played miserably and Oakley was taken out of the game for bonehead work and Manager Grim announced afterward that he would suspend the pitcher for the remainder of the season.
 
4 December 1909, Sporting Life, pg. 7, col. 2:
Cal Ewing pulled off the biggest “boner” of his career when he let the Northwestern League in here this last season.
 
14 January 1914, Wilkes-Barre (PA) Times Leader, pg. 14:
GAME MERKLE MADE FAMOUS STILL LIVES
Great Contest Between Giants and Cubs, Featured by Joe Tinker’s Wonderful Playingand Merkle’s Original “Bone Head” Play.
Walk up behind John J. McGraw, manager of the Giants, and ask him, “What happened on September 23, 1098?” and the chances are McGraw would swing hard for your jaw.
 
Because September 23, 1908, was the day Fred Merkle made the first of his trio of so-called bone head plays in a pinch; the day the Giants lost from $3,000 to $4,000 world’s series money each and the club owners about $50,000 of the same well-known United States kale.
 
Important as was this game, there is little knowledge as to what happened that day in New York; about all anyone remembers is that Merkle failed to touch the keystone bag and that Johnny Evers’ quick-thinking saved the game.
 
Merkle has been accused of running out of line before the winning run was scored; of turning to the left after passing first, which, in the opinion of many, made it necessary for him to continue to second on his own hit and of several other impossible base ball crimes. Here is what happened:
 
It was the last of the ninth, with the score 1-1 and the Giants at bat. Seymour was thrown out by Evers. Devlin singled, but was forced at second when McCormick hit to Evers. Then Merkle singled so far into right field that McCormick reached third base.
 
Bridwell hit the first ball pitched by Pfister, to center field and ran to first, while McCormick crossed the plate wit hthe run that should have won the game, but didn’t because of Merkle.
 
Merkle was subbing at first for Fred Tenny, being still a recruit player. On Bridwell’s hit he started for second, but when half way left the base line and sprinted for the clubhouse back of right field, to beat the crowd swarming upon the field in the belief that the game was over.
 
It was Bob Emslie’s place to watch the play, as he was umpiring on bases, but he was on his way to the clubhouse with the Giants, just as O’Day had been in Pittsburgh.
 
To this day Merkle, in upholding himself, says Emslie told him to go ahead—that the game had been won.
 
When Merkle started for the clubhouse, Evers yelled to Hofman, in center, for the ball. Instantly Captain Mike Donlin realized the situation and started after Merkle. Joe McGinnity, cutting across the field, caught the ball as it was thrown to Evers and was jumped upon by three of four Cubs. McGinnity tossed the ball into the crowd of spectators and Floyd Kroh, dashing into the crowd, rescued the ball and while he indulged in a free-for-all with several New York fans Steinfeldt and Tinker took the ball to Evers, who touched second base.
 
Donlin collared Merkle and was hustling him to second, but the rescue was too late.
 
The game went to the league board of directors, who declared it a tie and ordered it replayed .Chicago won the playoff and with it the league championship.
 
In the game Merkle made famous Mathewson outpitched Jack Pfister, fanning nine Cubs and allowing but five scattered hits.Joe TInker, now a Federal League manager, handled 15 out of 17 chances at short and it was his home run that gave the Cubs their only run.
 
17 June 1915, Lincoln (NE) Daily News, “Merkle’s ‘Boner’ Lives Forever,” pg. 9, col. 2:
Fred Merkle “puller a boner” that cost the New York Giants a pennant. That was years ago but the fans have never forgotten. “Bonehead” is hurled at him to this day. “Laughing Larry” Doyle was guilty of a thoughtless act fully as bad or worse than Merkle’s a couple of weeks ago but already his lapse of memory has been forgotten. It came in a game that didn’t particularly count. Which causes one to think, after all, it isn’t what you do that hurts—it is when you do it.
 
Merkle’s “bone,” as is well known, was in forgetting to touch second in order to complete a play.