Chad Qualls is a serviceable reliever, a sinker-slider pitcher who induces a high amount of groundballs and can rack up the strikeouts. I feel like I'm stating the obvious here, but Qualls has not had a good 2010 season. In fact, it is down right ugly. Among qualified relievers, Qualls has the highest ERA, opponent's batting average, BABIP, and second lowest left-on-base percentage in the Majors. This is after six solid seasons with the Astros and Diamondback, never posting an ERA above 3.76 the entire time.
Those stats I mentioned above - ERA, batting average against, etc - don't necessarily tell us how well Qualls pitched. Rather, they tell what happened, which is still useful. Looking at some DIP metrics - Defense Independent Pitching - this season Qualls has performed slightly worse than he has in the past, notably posting the highest walk and home run rates of his career. Other than that, saber-thinking tells us that his performance has been dictated by luck and should regress to his career levels.
Crawling out of the spreadsheets, Qualls had surgery last August to repair his dislocated patella in the left knee (the patella is the kneecap, ouch!). The left knee is the leading foot for a right-handed pitcher and becomes the planting foot as the pitcher delivers the baseball. Qualls might have felt some change in his knee after the surgery, enough to cause the change in mechanics that occurred this season.
Recently, Harry Pavlidis found that Qualls whiff and ground ball rates are also declining this bad season. This shows that there has been some change in how he has performed this season other than luck. Since he has only two pitches, it was easy for me to classify Qualls's pitches and to determine whether one pitch worsened more than the other.
Both pitches have been hit brutally hard when put into play, as evident by the high wOBA on contact (wOBAc), but he is second in the majors in wOBAc, so those numbers aren't surprisingly high. While the sinker has maintained a relatively consistent contact rate, the slider has been more prone to contact this season. It is vice-versa for pitches over the plate - his sinker has crossed the plate almost 10% less of the time this season than last. This is where his increased walk rate comes in, as he uses the sinker as his primary pitch (used over 60% of the time). And this problem with locating his sinker may be caused by altered mechanics.
In a nutshell, the Rays may be taking some risk here. Qualls has definitely had some bad luck go his way this season, but some other metrics suggest he may have lowered his performance as a pitcher. Whether this solely has to do with his surgery/mechanics, I don't know. Qualls has a good track record in the Majors as a late inning reliever and has good upside; the fact that his ground ball rate is still above 50% and he can actually get a strikeout, unlike groundball extreme Chad Bradford.
And I write this after he gets key ground ball from Lance Berkman in the eighth inning* with one out and a runner one first. A double play after falling behind 3-0. It may just work out after all.
*Written prior to this recent series.
Data and stats from Fan Graphs and MLBAM.