You probably noticed that the Tigers are not scoring a lot of runs in 2010. Indeed, they are averaging just 4.34 runs per game (RPG). However, there are a lot of teams not scoring runs this year. A total of five teams in the American League have scored fewer runs than the Tigers and the league average is only 4.47 RPG. That is down 7.3% from 2009 when the league averaged 4.82 runs.
While there is year to year variation, the chart below shows that there has been a general downward trend in run scoring over the past decade. AL offense is down 10.0% from from 2006 (4.97 RPG) and 15.7% from the height of the home run derby era in 2000 (5.30 RPG).
Offense is also declining in the National League but not by quite as much. There have been 4.36 runs per game in the NL this year which is not much different from the 4.43 RPG in 2009. Over time, run production in the senior circuit is down 8.4% since 2006 (4.76 RPG) and 12.8% since 2000 (5.00 RPG).
The reason for the sharper decline in AL could just be random variation, In other words, it could just be a down year for offense in the AL. It will take a couple more years to see if the offensive output of the two leagues has really become that close. If it is a real trend, one explanation might be that AL teams are trying to keep up with the The Yankees by emphasizing defense, which has become cheaper than offense in recent years.
Regardless of any differences between the leagues, it is clear that the we have come a long way since the crazy offense of ten years ago. In fact, fewer runs have scored in 2010 than any year since 1992 (4.32 RPG in the AL and 3.88 in the NL). What we have today is a more balanced game between run scoring and run prevention than we had in 2000. I believe this makes for a more entertaining game with a greater variety of teams and types of players.