MLB: How baseball has changed over the decade

This MLB season concludes a decade of profound changes throughout the game

The MLB game of 2029 will be substantially different from the game we watch today.
How? That can’t be predicted. But given baseball’s constantly evolving nature, change is inevitable.
A review of the numerous profound ways the game has changed merely since 2009 illustrates the inevitability of these changes, which have occurred on the mound, in the field, in the batter’s box, in the dugout, in the front office…and in some cases even in the ballpark’s environs.

We can measure those changes both in numbers we are familiar with and also in numbers that didn’t exist in 2009. Just to pick a couple: in 2009, the average hitter batted .262; today he hits .252, nearly a 4 percent performance decline in that metric. On base average is also down, from .333 in 2009 to .323 in 2019.

Perhaps confusingly, ERAs have risen even as batting averages have fallen off. In 2009 the average ERA was 4.31; during the just-completed season, it was 4.49, about 4.2 percent higher. The reasons for that seeming dichotomy between declining batting averages and rising ERAs have everything to do with more profound changes in the game’s play, and will be discussed momentarily.

MLB ballplayers are, as a group, younger. Perhaps a byproduct of the generally higher salaries earned by more veteran players, the average age of a 2019 player was 28.1 years, about six months younger than the 28.6 year average age a decade ago.

Those, however, are merely the superficial, and generally the smallest, changes. Far, far more important have been the ways in which teams research, plan and execute a season, and also the methods they employ to make player personnel decisions.