Mike Axisa at RotoGraphs looked at how Adrian Gonzalez is losing some home run power as the season has gone on.
The lack of power can examined further by looking at his batted ball distance of home runs and fly balls over the past 3 years including 2011 splits:
Year - Distance
2008 - 308 ft
2009 - 301 ft
2010 - 291 ft
3/1/11 to 6/17/11 - 295 ft
6/18/11 to 8/11/11 - 278 ft
Adrian has continued to hit the ball with less and less distance over the last 3 years. This decrease can be seen in this graph of his batted ball distances over the last 3 years:
Besides not hitting the ball as far, he is not turning on the ball as much has seen by the angle (-45 is the LF line and 45 is the RF line) on the field that the ball landed:
Adrian is also not turning on the ball as much as the season has gone on.