Back in June, I wrote a post about how AL run scoring had declined in the first half of the year to 1992 levels. Despite some speculation that run scoring would rebound in the warm summer months, second half run scoring was actually significantly lower than first half, and the AL finished at 4.45 runs scored per game. An updated graph:
For whatever reason, run scoring plummeted this year back to the levels last seen before the home run era. I’d suspect that it partially cyclical (a wave of talented young pitchers has arrived) and partially due to teams better valuing defensive players, but also an effect of performance-enhancing drugs exiting the game. Health might also be important. Factors that make it easier on pitchers tend to cascade, as pitchers who take less of a beating pitcher longer into games, which means the worser members of a bullpen pitcher less, which lowers ERA.
But the significantly different environment really does change how we evaluate players. The average hitter batted .260/.327/.407 in 2010, but .267/.336/.428 in 2009. That difference helps to make the decline of players like Alex Rodriguez, Mark Teixeira and Derek Jeter more drastic, and disguises how big of a step forward players like Nick Swisher, Brett Gardner and Robinson Cano made. On the other hand, it makes the performances of Phil Hughes and A.J. Burnett seem that much worse. Statistics indexed to the league average, like ERA+ and OPS+ become that much more important. Also, rough calculations on the back of the envelope for things like WAR and wins should use 9 runs per win as a baseline instead of 10 runs per win.
Also, the gains from things like stolen bases, bunts, hit and runs, etc become more pronounced. Leverage becomes more useful as ballgames are tighter, so teams with stronger bullpens will reap some advantages. Its also theoretically easier to break in young pitchers, who will be entering a more forgiving run scoring environment. All of these probably net benefit the Yankees more than their opponents, so this is all good news.