The end of Major League Baseball’s performance-enhancing drugs era is causing 1960s flashbacks.

With the baseball season almost halfway complete, 23 major- league starting pitchers with at least 10 appearances have earned run averages below 3.00. In comparison, there were 12 in 1998, when Mark McGwire and Sammy Sosa’s season-long home-run duel marked the era of steroid use in the sport.

– Mason Levinson, Bloomberg.com.

There’s been a ton of talk this season about how offense is down and how it’s “the Year of the Pitcher” and everything else. A lot of that has to do with the perfect games and no-hitters, but others have pointed to a league-wide decline in offense prompted by the end of the so-called Steroid Era.

I’m not buying it. But we have graphs to help us visualize data a little better, so I plotted out the league-average runs per game (per team) since 1980. It looks like this:

So yeah, runs are down a little this year. It’s important to note, though, that we’re only dealing with half a season worth of data for 2010, and that offense tends to pick up in the summer months as the weather heats up and balls carry more.

Plus, there’s a lot of noise here, enough so that a fluctuation of .15 runs per game really doesn’t seem all that strange.

Total runs are definitely down from the 5+ run years in 1999 and 2000, but they haven’t really been steadily decreasing since 2002. And baseball implemented tougher performance-enhancing drug testing in 2004.

And for all the talk that the steroid era prompted the offensive explosion of the late 90s and early aughts, it sure looks to me as if the big change came around 1993, when baseball expanded to Miami and (whoa, nelly) Colorado.

Did players happen to start juicing that same year, or did the watered down talent pool lead to more runs? Or is it a little from Column A, a little from Column B? And how much impact did Camden Yards (opened in 1992) and all the hitter-friendly parks that followed have?

Maybe the “Year of the Pitcher” in 2010 does have something to do with all the talented young pitchers that have entered the league. Or maybe it has to do with a few new pitcher-friendly parks, early-season weather, the recent emphasis on run prevention and random fluctuation.

Rob Neyer wrote about the same subject today and called it “a puzzle” that no one “has come close to putting together.”

But I wonder if there’s really one solution to be found, one distinct way to solve the puzzle. Neyer cites the interesting uptick in strikeouts this season, which is certainly interesting. Could that be due to better scouting thanks to better technologies? More thorough understandings of hitter tendencies? Or could it be the residual effect of years of work by people like Neyer himself to destigmatize the strikeout for hitters?

I’ve got nothing. All I know is that baseball is in constant flux, and strange and random things happen all the time. We’re still not even halfway through the season. I’m not ready to call this anything yet.