In the 1921 World Series, the New York Giants beat the New York Yankees five games to three. This was the last of the experimental best-five-of-nine series. his was the only Series prior to the 1955 World Series (Brooklyn Dodgers over New York Yankees) where a team losing the first 2 games went on to win the Series
The Series was much-anticipated, as it featured John McGraw's Giants, who were dedicated practitioners of the dead-ball era's "inside game"; and the Yankees, who relied on the "power game" exemplified by their star player, Babe Ruth, who was coming off a sensational year, arguably his best ever statistically. This was Ruth's 1sst World Series as a starting outfielder. (He played 2 innings there in the 1918 World Series when he was used as a starting pitcher for the Red Sox. Injuries suffered during the Series would limit his effectiveness significantly. However, this Series marks the start of the Yankees dynasty, as it was the first of 39 American League pennants as of the 2008 season.
Despite Ruth's limited action, the Series was a closely-contested matchup. The Series ended on a double play featuring a baserunning miscue. Because of an infected arm and a bad knee (he wrenched it in the fifth game), Babe Ruth did not start the final game but did appear in the bottom of the ninth pinch hitting for Wally Pipp.
For the first time in World Series play, all games were held at one site: the Polo Grounds in New York, with the home team alternating. The Yankees sub-leased the Polo Grounds from the New York Giants from 1913 through 1922.
The Series was the first to be broadcast on radio. Announcer Thomas Cowan recreated the game over Westinghouse-owned WJZ in Newark, listening to phoned-in reports from the stadium. (Answers.com is wrong in attributing this first broadcast to sportswriter Grantland Rice—Rice announced the 1922 World Series over WJZ the following year.) 
Following the Series, Ruth and Bob Meusel participated in some post-season barnstorming, which was then against the rules for Series participants. Both were suspended for the start of the 1922 season, but Ruth made a personal appeal to Commissioner Landis. He upheld their suspensions, but agreed to rescind the rule effective with the end of the 1922 season.
One of the highlights of the Series was the relief pitching of New York Giant pitcher Jesse Barnes, who was the first pitcher to 2 games in relief in one Series.He struck out 10 men in relief in Game 6, the record until Moe Drabowsky of Baltimore sturck out 11 Los Angeles Dodgers in Game 1 of 1966 World Series.