Recently, my research focus has been on pitching dominance and pitching speed. The folks over at Fangraphs.com have a great database showing pitch type/value to include speeds and movement on a variety of pitches from Baseball Info Solutions.
The "pitch type" list shows the average speed for each of seven pitches and one column categorized as "miscellaneous or XX". Slicing though the fastball speed data, I noticed that the top fastball speeds seem to increase year to year over the 9 years listed (since 2002). This was also true for the "average fastball velocity" hitters were seeing during the course of each season.
Each list was very long so I stream-lined the data showing the number of players who saw average fastball velocities at or above 90, 91 and 92 mph. I picked these velocities because its been documented through research by Mike Fast over at Hardball Times http://www.hardballtimes.com/main/article/lose-a-tick-gain-a-tick/ which shows that for every 1 mph increase in velocity, starting pitchers give up 0.26 less runs or 1 run for every 4 mph increase in velocity. Relief pitchers, the amount is 0.42 less runs or 1 run for every 2.5 increase in mph.
The graph below shows the data since 2002
The increase in players who see fastballs above 90 mph over the course of a season is increasing but not as dramatically. The real increase is with the number of players who see fastballs above 91 mph. In 2002, no player saw average fastball velocities above 91. 2005: 2 players; 2008: 38 players. Here is the real jump. 2009: 120 players, 2010: 128 players and this year so far: 117 players.
Fastball speed by itself is not the only driver of the decline in offense. But over a year, or in this case 9 years, there is strong evidence to support the argument that fastball speeds are increasing and they are contributing to a reduction in runs.