Sabathia didn't have his best slider in the Yankees' opener yesterday. His location was off as it hung up in the zone quite a bit. Over the last three seasons, batters have made contact on his slider 56.1 percent of the time. On 24 sliders yesterday afternoon, the Tigers made contact 77.8 percent, primarily on pitches in the strike zone. Obviously, it's only one game's worth of data, but it was clear he wasn't able to keep the pitch down like he normally does.
BrkX and BrkZ values provided by PitchFX measure the number of inches the ball moves horizontally and vertically as a result of the spin on the ball read from when it is 40 ft from home plate. Sabathia traditionally gets about 5.1 inches of BrkX (horizontal) movement on his slider. Yesterday it averaged 2.8 inches. From 2008-2010, PitchFX data has Sabathia throwing 2060 sliders in regular and postseason games combined. Only 450 of those sliders have had a BrkX reading less than 3.0.
One game's worth of data is not enough to draw any significant conclusions on one pitch. Besides, it was cold, and CC usually takes a few starts to get going. If he's still hanging his slider up in the zone in a couple weeks, then it might be time to worry.