Much of the Rays' shortcomings this year has been placed on the defensive errors and injuries up and down the lineup, but the biggest reason for the month plus of subpar baseball has been the (lack of) offense.  The above chart shows how each player has fared this year through the lens of wRAA.  This stat is great because it shows how each player has outhit the average batter based on wOBA and plate appearances.  In this instance I have compared each player's wOBA at each position compared to the position's American League average wOBA to better reflect how each batter has performed relative to their peers at each positions.  Here's the league average numbers:

We can look at Pena as an example of this, as his .332 wOBA over 347 PAs works out to a -2.4 wRAA compared to the AL average 1B wOBA of .340.  You can look at these across the board, but you'll quickly notice that Zobrist, Joyce, and Longoria are the only players that have been better than their positional peers across the board.  Elliot Johnson has been a nice surprise as well, but guys that we've counted on like Upton, Jennings, Rodriguez, and all of the catchers have not hit as well as their leaguemates.  Some may find it easier just to look at the numbers instead of the chart:

Again, we see that 2B and SS have been slightly better than league average and RF has been a monster position for the Rays, but that's it.  Every other position has contributed A LOT to be desired with the sticks and their gloves haven't exactly made up the difference.  Injuries are certainly to blame as some of these guys on the right would have never seen the roster, but the bigger impact is from players that needed to step their game up in the absence of the big guns and that just hasn't happened.