Declining Strikeouts
Sabathia had a solid K/9 in his rookies season of 2001 at 8.53, but that fell to the mid 6's from 2002-2004. He began to climb again in 2005 and reached 8 again in 2006. He reached 8.93 for 2008 and it was that high before he even went to the NL. This year though it has fallen to 6.58 and although May and July it was over 7 it has never reached 8.
Pitch Values
Looking at pitch values doesn't always tell the whole picture, but it can give us some insight. His fastball has always had league average value, but in his better seasons his slider has always been much better. Last year his slider had a 3.56 run value per 100 pitches while this year the slider is average at a 0.62.
Yankee Stadium
Any struggling pitcher of course could look to Yankee Stadium to explain any ills. This actually has some potential as his rates are very off at home this year. While his overall K/9 is 2.41 his K/BB at home has been 1.95. That isn't a small sample size either at 62.1 IP.
This could be any number of things, but it has his home FIP at 3.98. His overall FIP is 3.70, xFIP is 4.28 and PAxFIP is 4.21. His road numbers are still not as good as last year, but show he is still having troubles at home. Perhaps with the effects on homers he is trying to much to pitch around hitters and that is causing hitters to swing less at pitches out of the zone (26.5% O-Swing%, lowest level since 2005).
He may not be the top 5 pitcher many drafted him as, but he is still a solid pitcher. You can't give him away and he is still going to rack up wins on the Yankees. His rest of the season ZiPs projection calls for 8 Wins, 3.31 ERA, 99 K and a 1.23 WHIP.
