Nationals Sign Chien-Ming Wang

Yankee fan here myself too (since the early 1980’s), as you’ve said it, he relies in his SINKING pitch (just what i said), not the fastball per se, not a stone thrower as Joba, as Huges, as Clemens, besides the usual fastball (even hitting 95MPH on occasions), he uses his sinker looks like a fastball but with a lot of downside action. As you see, the fact that his fastball has remained almost the same is what gives us an insight about what could be wrong:

2007 93.7 MPH average
2008 91.8 MPH average
2009 92.2 MPH average

BUT when you check his offspeed pitches, you can see there’s no apparent difference in the past two years:

2007 Slider speed 84.3 MPH, Changeup speed 81.3 MPH
2008 Slider speed 85.9 MPH, Changeup speed 83.5 MPH
2009 Slider speed 83.2 MPH, Changeup speed 83.1 MPH

As you see when both offspeed pitches are at the same velocity, MLB players can succesfully time Chien Ming pitches, in the other hand, the fact that both his fastball and sinker are almost at the same velocity gives him the upside because players don’t know wheter to swing and adjust for a sinker of a plain fastball. But with the movement being diminished, they waited for offspeed pitches, knowing that, at best, both had the same movement and velocity.