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Follow-Up Intro to BaseballVMI

Posted: 2019-04-23 12:18:55 (ET)    [ 725 views ]


In my last blog article, I introduced the concept of ADI (the air density a game is played within) and the VMI (the Visual Memory of a hitter in MLB).  In Major League Baseball the ADI is affected by the altitude air pressure, the temperature and the humidity at game time.  All three of these ingredients in air fluctuate during the day but remain reasonably stable during the contest.  

Utilizing the “Neeley Scale” which is primarily earth surface air density, all of MLB plays between approximately 40 at the light end of the scale in Colorado and 80 in the heavier air at sea level. 

If the air is heavy the pitches will be more reactive in terms of movement as they speed toward the strike zone.  We call the heavy air venue’s and the colder gamedays at sea level “Heavyweights.”   Colorado is a “Featherweight” in terms of air density, but on cold days can jump into the “Lightweight” categories of Atlanta, Texas and Kansas City on those teams' hottest days.   The Central Division tends to bounce from the “Heavyweights” in April to the “Welterweights” and finally to the “Middleweights” in the heat of the summer.  These various weights of air regardless of whether it is caused by altitude, temperature or humidity allow the pitcher more or less movement by up to 4 inches on the four-seam fastball in MLB ballparks. 

If a hitter has been hitting in a Heavyweight air for a series, his elbows must be positioned higher (in his initial stance and pre-swing) to be prepared for the 4 inch extra lift on the four-seam fastball, than in Lightweight air.   So, the lesser lifting, but further sliding two-seamer will then, be a good groundball producing pitch for the pitcher to use.  
Conversely if a hitter has been in Colorado for an entire series and played all three games, hit the ball relatively well, then his elbows have relaxed downward by a few inches to prepare to swing at the lesser lifting four-seamer.  So, if the ensuing pitcher relies on the two-seamer, then the hitter’s stance and pre-swing will put his bat squarely on the two-seamer in Welterweight air even if it slides more so and he hits it off the handle or the end of his bat.  But generally, it is a pitch that should be used sparingly and cautiously against such a team.

These two examples identify the extremes of the VMI.  In the first example the VMI would calculate to a high Plus VMI because when he leaves sea level to go to, say Atlanta, his pre-swing stance would put his bat above the center of the ball.  In the second example the VMI would calculate to a high Minus VMI because when he leaves Colorado to go to a place such as Arizona his pre-swing stance would put his bat below the center of the ball at the zone.  In this case, the Minus VMI would identify a hitter (actually the entire team) as potentially dangerous against downward breaking pitches, but anemic against the 4-seamer.


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