His splitter lost so much velocity (from 89.3 MPH in 2011 to 83.7 MPH in 2012) that he was forced to abandon it almost entirely (going from throwing it 12.4% of the time to just 2.1%). There aren't a lot of pitchers who throw the splitter, but among the 11 qualified starters in MLB who do, Fangraphs' PITCHf/x data (all pitch data here comes from Fangraphs' PITCHf/x boards) has Jimenez's splitter rated as the very worst in 2012.
He also threw fewer two-seam fast balls, leading him to rely more on his four-seam pitch, which fell from 96.2 MPH in 2010 to 93.9 MPH in 2011, to 92.5 MPH in 2012. This loss in velocity crushed the value of his fastball. In 2010 it rated as the second best pitch of any qualified starter in baseball. In 2012, it rated as the 6th worst pitch.
2012 in Review: Ubaldo Jimenez
Let's Go Tribe | Oct 3