This is more of a must-click-link kind of thing in that the question is being asked and answered in this article from Rob Arthur and Ben Lindbergh at FiveThirtyEight.
The short version: offense spiked last year, primarily in the second half. Almost all of the spike came on the back of home runs. The increased home run rate was not attributable to weather, relative talent-level between hitters and pitchers, or a variation in the strike zone or balls and strikes thrown.
That leaves two potential explanations: (1) random chance; and (2) the baseball.
Was the baseball tampered with to make it more lively in the second half? Some suspect just such a thing happened in the past (I’m lookin’ at you 1987 and 1993-on). Arthur and Lindbergh tested that hypothesis. With the help of a freakin’ cannon and a university research lab no less.
I won’t give away the results, but they definitely give us reason to watch the beginning of the 2016 season closely.