May 5, 2013; Arlington, TX, USA; Texas Rangers relief pitcher Joe Nathan (36) pauses between pitches against the Boston Red Sox in the ninth inning at the Rangers Ballpark in Arlington. The Rangers won 4-3. Mandatory Credit: Jim Cowsert-USA TODAY Sports

What Is Wrong With Joe Nathan?

On the surface, Joe Nathan‘s 2013 season thus far does not seem to be anything out of the ordinary—20.1 IP, 2.21 ERA and 8.41 K/9, but beneath the surface, there exists true cause for concern.

On the spectrum of facets of Nathan’s 2013 season that are worrisome, his drop in velocity is probably the most negligible, but it is worth noting. In 2013, Nathan’s average fastball velocity sits at 91.7 mph, as compared to his average fastball velocity from 2012 of 94.0 mph. Strangely enough, hitters are only hitting at a .083 clip against Nathan’s fastball despite the dip in velocity, but this due to an incredibly low BABIP of .063 against the pitch (for reference, Nathan’s fastball has drawn a BABIP of .220 for his career). Furthermore, Nathan has shown a noticeable dip in velocity with his slider as well—average slider velocity of 85.6 mph in 2013, as compared to 88.5 mph in 2012. But what is most strange about Nathan’s slider in 2013 is not the dip in velocity, but the sudden increase in vertical break with the pitch. For his career, Nathan’s slider has exhibited a 2.8 z-MOV (z-MOV measures vertical movement, so for example, a pitcher with a big breaking curveball would post a negative z-MOV). In 2013, Nathan’s slider has shown more vertical break—0.8 z-MOV, which is completely out of the normal for Nathan’s career. What affect this will have on Nathan’s season going forward is truly difficult to tell, but it does give the indication that there is something that Nathan is doing differently, whether it be purposely or not.

Perhaps what is the most alarming facet of Nathan’s 2013 season is his declining GB%. In 2012, Nathan posted a GB% of 45.4, as compared to a GB% of just 25.5 in 2013. Nathan has yet to show difficulties when it comes to an increased rate of surrendering homeruns in 2013, but with such dips in velocity to go along with a declining GB% and career-low BABIP of .208, this recipe could ultimately lead to trouble.

What is wrong with Joe Nathan is quite simple, he’s aging and is on the decline. As mentioned before, Nathan’s 2013 season has yet to appear troublesome on the surface, but there are noticeable differences across the board. Based on these aforementioned figures, it is not a matter of how effective Nathan is at the moment, rather how long before he implodes.

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