This season has not been kind to CJ.  After a quick start, his recent struggles has been well-documented.  Here I will try to raise a view possible points of discussion as to what is wrong with him.

Before you start, first read the excellent article at Baseball Time in Arlington by Mr. Matschulat Here

Recapping a few points from the above article:  CJ is throwing more fastballs, more strikes, does poorly in stranding baserunners.  He also has low BABIP and low line drive %.  His strikeout numbers are low.

For this reason, it is fitting to start with the fastball.  CJ is throwing the fastball 86.6% of the time, way up from previous years.  They average 92.4 mph with average horizontal and vertical breaks of 5.92 and 9.58 inches.  35% of them are balls, and 6.5% of them are swung and missed.  (see the movement chart below)

Well, really there is nothing wrong with this picture.  The fastball has good velocity and very good movement.  By all means, it's a good fastball, and the fact that he is throwing 65% strikes means he has at least decent command of it.  Since he throws it so much and does not get much strikeouts, the low BABIP implies that most of the time, hitters do not get very good wood on these either, but what about the ones that they do hit?

Well here is a crude graph of the locations of pitches that resulted in hits for CJ so far this season.  All of these pitches except for 1 are fastballs (the other one is a curve).  Not surprisingly, the ones that are hit are pretty much at the middle of the plate.  More surprising though is the circumstances under which they are hit.  Of the 15 hits, 8 are doubles or HRs, and only 1 of these 8 ABs that resulted in double or HR saw more than 3 pitches (the exception was 4 pitches).  6 of these 8 hits were in counts favorable for the pitcher where CJ threw a fastball.  In contrast, only 2 of the 7 ABs that resulted in singles had less than 4 pitches.  What one can conclude from this is that extra base hits are consequences of hitters seeing the pitches they wanted while singles are mostly result from hitters battling it out.

Now looking at the breaking pitches, we find something interesting.  CJ throws essentially 3 breaking pitches, a slider, curveball, and changeup.  So far he has thrown 10 change, hitters have swung at 2 of these pitches, and 7 were balls.  He has thrown 19 curves, and hitters swung at half of them.  Finally of the 12 sliders, hitters swung at only 3 of them and 7 were balls.  These off-speed pitches are designed to generate poor swings by hitters so they can't sit on the fastball, and the fact that they are NOT swinging at the off-speed pitches is troubling.

Here is another crude chart of the locations of off-speed pitches.  CJ is able to locate the curve fairly well, and to some degree the slider, but he does not throw the slider and change for strike, and the hitters aren't bothering with them.  This means that he is essentially reduced to a 2-pitch pitcher, and hitters will just sit on the fastball and/or curve.  In fact, most of them are not very successful at hitting the curve, so they are just looking for the fastball. 

This could be where the problem lies.  Since CJ throws so few off-speed pitches, and does not generally throw them for strikes, hitters can afford to ignore those pitches and concentrate on the fastball.  Not only this, they can sit on certain locations so that CJ can't get away with too any mistake fastballs down the middle (which is why the hits are hit hard).  Also, most of those breaking pitches are thrown on 0-2 and 1-2 counts, but since they are not thrown for strikes and hitters do not swing at them, it's useless a lot of the times.

I for one would like to see him throwing the change and slider for strikes more often.  This will hopefully throw hitters off his fastball, and force them to swing at a few more off-speed pitches.  His release point for all of his pitches are similar, and he should have success with them.