Manny Acta suggests hard throwing pitchers are responsible for the decline in runs scored (original quote here):

”I can’t remember when so many people were throwing in the mid-90s and even 100,” Acta said. ”Just about every team has a guy who gets close to 100, if not in the big leagues, then in the minors. Men must be evolving.”

According to data available at Baseball Analytics, there are 16 pitchers with at least 100 pitches thrown who are averaging 95 MPH or better on their hard pitches. That’s exactly where we were last year at this time, games were producing about 1/2 a run more. I don’t think it’s hard throwers, although it’s a good theory.

(At this point last season, 295 pitchers had thrown at least 100 pitches, and they averaged 91.1 MPH on their fast pitches. The median was 91.2 MPH. This season, 255 pitchers average 91.3 MPH on their hard stuff, with a mean of 91.5. So as a group, there is a bit more speed. Two years ago I showed that until fastballs get up to around 97 MPH, batters handle them well.)