## Beyond CERA: The Sabermetric Case for Rob Johnson

I am new to this forum, so it has taken me some time to become acclimated.  Visiting a blog community is much like visiting a foreign land -- one has to make an effort to learn the language and customs.  Like a traveler in a far away land, however, I feel that not only do I have much to learn from you, but you can learn from me as well.

One custom I have noticed here is that everyone seems to enjoy putting down Rob Johnson.  I think in a community like this one, it is easy to develop a sort of groupspeak echo chamber.  One person puts down a player, and then another, and then another, and before long, the entire community is down on that player without really thinking about it and evaluating their play objectively.  I feel that has happened here with Rob Johnson.

I know you all like to poke fun at Rob Johnson's batting average, and his CERA in order to "prove" that he is a below average major league baseball player.  While I think those statistical tools have their place, I believe that we can all work a little harder to learn more statistical tools and refine our understandings.  I think if you all open your minds and make a concerted effort to educate yourselves, you will change your view of one of my favorite players -- Rob Johnson.

Many baseball analysts and, frankly, many fans, use statistics like errors and fielding percentage in order to evaluate defense -- even catcher defense.  But I am here to tell you that those tools do not tell the whole story.  Statisticians have much more sophisticated tools now that break down individual plays and can help tell us which players on a field at a given time are responsible for which outcomes.  This is important because it helps illuminate repeatable skills, which tell us how players will perform moving forward.

One of the things that Rob Johnson does well, for example, is catch curveballs.  There is a lot that goes into determining the success of a pitch (speed, location, sequencing, delivery), but for a curveball the catcher is of the utmost importance.  The catcher of a curveball can affect how much the spin causes it to deviate from a spinless trajectory, and is commonly broken up into catcher horizontal and catcher vertical components. So the catcher vertical movement is how much a pitch sinks or rises compared to the same pitch with an average catcher. The catcher horizontal movement is how much a pitch tails horizontally compared to expectation with an average catcher. Positive catcher horizontal movement indicates a catcher who causes a pitch to tail away from a RHB and in to a LHB.

I have taken the initiative, using a MLB service called Gameday PitchFX, to record the vertical and horizontal movement of curveballs thrown to Rob Johnson, versus those thrown to the other Mariner catchers:  Kenji Johjima and Jamie Burke.  Here are the movements of curveballs caught by those catchers. The gray dots are the movement of all curves for reference.

As you can see, curveballs thrown to Rob Johnson have a wide range of movement, but generally lots of horizontal movement (tailing away from RHBs an average of about 6 inches) and not much vertical break.  Curveballs thrown to Burke have lots of vertical and horizontal movement, sinking and tailing away from RHBs by almost 10 inches in each direction.  Johjima-caught curves have little movement what-so-ever (his curves are very close to 0,0).

These advanced statistics, Catcher Vertical Curveball Movement (CVCM) and Catcher Horizontal Curveball Movement (CHCM), tell us something we cannot glean from rudimentary statistics like CERA.  If you were a pitcher, and you could throw to one catcher who does not improve the break of a curveball (Johjima) and another catcher who does (Johnson), which one would you choose?

Jamie Burke-caught curveballs have the most movement of all, but he is not considered a very good candidate to be the Mariner catcher because he has low CFBV (Catcher Fastball Velocity).  That is to say, that Jamie Burke-caught pitches have a high correlation with low fastball velocity.  This is a glaring weakness in Burke's game and will be the subject of a subsequent post.

But the comparison between Johnson and Johjima is telling.  I am confident that if this community were to have an open mind to advanced statistics such as this, it would share my view that Rob Johnson gives the Mariners the best chance to win.  Let's all try to improve our statistical analysis, or we will fail to appreciate that one of the better catchers in the game is right here in our own backyard.

***

UPDATE:  I really appreciate the outpouring of support in the comments section.  Clearly, I underestimated the openmindedness and sophistication of this blog community.  It is great to see so many people willing to admit that they were wrong before.

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