SABR's Paul Wendt posted a pdf of a fascinating article by F.C. Lane titled "Has the 'lively' Ball Revolutionized the Game?" The article appeared in the September 1921 issue of Baseball Magazine.
I've written about F.C. Lane before, a man who was in many ways ahead of his time (particularly in his understanding of performance analysis), and you can read about his fascinating book Batting here.
As was the case with many in and around the game during this period, Lane grew up when pitching dominated and so it's not surprising that he viewed the exploits of Christy Matthewson, Smokey Joe Wood, and Walter Johnson as normative and was alarmed at the era that Ruth was then ushering in. In this article Lane writes about what he considers the "foremost problem in baseball today."
He puts it this way.
"And since we all know that pitching is the bed rock of baseball, when we disturb the foundation of the game, we shake the superstructure."
Because of his knowledge and reverence for statistics he also rightly compares the inflation of batting statistics to the devaluation of currency during the war - a problem our own generation is now coping with in the "Lively Player Era". The article then explores the various reasons given for the devaluation.
Lane begins by reporting on his investigation of the ball itself in order to quelch the rumors that it is being manufactured differently and that the owners are responsible - a charge by the way that is recounted by Leonard Koppett in his book The Thinking Fan's Guide to Baseball in chapter 28 where he says that in "1920 the ball was made livlier again...That bit of history is well known." Apparently Lane would have disagreed.
In any case Lane toured both Reach (the ball used in the AL) and Spalding (that used in the NL) factories and concluded that the balls themselves were manufactured in exactly the same way, albeit with better materials and particularly better quality and more elastic yarn since the end of the war. He also specifically dismissed those who claimed that the balls were being made livlier on purpose, reporting on his interviews with the league presidents. In the end his conclusion on the manufacture of the balls was that:
"The ball in use in both major leages is actually somewhat livlier than it was during the war period due to better materials and possibly better workmanship. But there is no evidence of any great change in the ball itself from year to year."
He then went on to discuss the four other factors he saw as also contributing and that in sum were more important than differences in the ball itself.
"Ruth is more than a slugger, he is a homerun hitter. Fortunately for him, he began as a pitcher. A pitcher is not expected to hit. Therefore, he can follow his own system without managerial interference. Ruth made the most of this opportunity...I have tried to make myself a batter, which is something quite different. A batter is a man who can bunt, place his hits, beat out infield drives, and slug when the occasion demands it, but he doesn't slug all the time."
To me, and contrary to Koppett who views changes in the ball as most important, this factor is the first among equals. In Batting Lane also attributes Ruth's ability to hit homeruns and others ability to follow his example to adopting a particular style or "speciality" of hitting rather than the influence of different baseballs. The style that Ruth popularized along with the fact that the reluctance of owners to make rules that handicapped Ruth in light of the Black Sox scandal served to usher in the new slugger's era.
In conclusion Lane then discussed what he saw as minor contributing factors. He mentioned that it was becoming more common for fans to keep foul balls where once they were forced to return them which had the consequence of introducing many new balls into play. He also noted that the transition to the new pitching rules had caused pitchers to temporarily fall behind in the arms race and that soon they would develop new strategies to cope. The latter introduction of the slider and the resurgence of the knuckleball are two examples of how pitchers did finally adapt. Finally, he also mentions that hitters had grown in confidence from the abolition of the freak deliveries, which in the past had them more fearful of injuries.
In the end Lane I think correctly attributes the rise in offense to, for him, this unhappy confluence of factors and seems to look forward to the day when pitching would regain prominance. There is a parallel here to our own day where the confluence of factors including weight training, steroids, perhaps lower seems on the ball, the effect of aluminum bats on the training of pitchers, and the abscence of intimidation among others, have all contributed to higher offensive output. And as in those days there are those like Koppett who continue to believe that the ball was made livlier starting in 1993 despite tests that shows the coefficient of restitution hasn't changed.