When the Mets go about choosing which closer to pursue, and potentially extend an offer, not only has K-Rod's velocity diminished over the past few years, but according to Elias Sports Bureau, Rodriguez registered 1-2-3 frames in a career-low 29.2 percent of his innings. That ranked 151st out of 253 pitchers who worked at least 60 innings in 2008. Fuentes (41.3) was 13th, Wood (38.1) was 28th, Street (38.0), even with diminished stuff, was 29th, and another free agent, Brandon Lyon (37.7) was 31st.
It has been exceedingly noted that K-Rod's fastball has lost a bit of its zest, and most attribute that to his violent delivery. As read here , K-Rod's agent, Paul Kinzer, claims the reduction in speed has been a conscious effort to make his change-up more effective, not due to arm trouble.
Being that Rodriguez is only 26, his lack 1-2-3 innings might make the Mets cautious.
For more on this, check out Joel Sherman's article.