The Physics of a Juiced Ball   (04/23/01)
 
 

When McGwire started hitting home runs at a ridiculous pace in 1998, it called attention to a phenomenon that many people had been theorizing about for a couple of years: why were so many home runs being hit?   There were all sorts of theories, from smaller ballparks to bad pitching.  A lot of retired baseball players suggested the ball was wound tighter than it used to be.  In effect, that it was "juiced".  Last year, I examined each of the different theories and came to the conclusion that the reason for the dramatic increase in homers was that the batters were using "faster" bats and that the pitching talent hadn't caught up to expansion yet.  Well, it turns out there's more to the story.

I ruled out the "bigger batter" theory because the rates jumped overnight after the 1993 season.  In 1993, there were 5 batters who hit 40 or more homers.  When the stoppage ended the 1994 season, there were 14 batters who had legitimate shots at 40 homers.  That is, they had hit 27 already, with roughly 50 games left to play.  In the shortened 1995 season an equal number of hitters were on pace for 40.  In every year since, there have been at least 15 players who have hit 40 homers in a season.  So in the winter after the 1993 season, did players all of a sudden bulk up thinking that they needed to get their home runs in before the impending work stoppage?  Probably not.  When the number of top home run hitters increases by 200% in one year, it's more than likely there's something else at work other than "they just got bigger".

I also ruled out the "smaller ballpark" theory.  Ebbetts Field was small by today's standards as was Shibe Park.  I don't think any of the new ballparks are any smaller than they were.  And how does one explain the Colorado effect?  The Rockies joined the National League in 1993 and yet homers stayed relatively consistent.  Mile High Stadium increased home run output by almost 30%.  Yet the increase in 40 home run hitters from 1992 (2) to 1993 (5) was relatively small given the stadium's overall effect on hitting in the NL.  And that certainly wouldn't explain why the number increased by 9 more hitters the following year.

And lastly I ruled out the "juiced ball" theory.  Many were sure that because that balls were no longer wound by hand, but by machine, that the balls were much more compact and tighter, giving them additional distance.  Well, that might have some effect, but it's doubtful that the effect would be more than a couple of feet in overall distance.  However, I'm not even sure the new balls are more compact.  I recently held a ball from the 1924 World Series and it's stitches were much flatter than any of the balls I have from recent years.  If anything, that ball was more aerodynamic than the modern ones.

So all I was left with was that batters were using faster bats - that is, they were shaving down the handles to make them lighter and more aerodynamic for increased bat speed - and that the influx of pitching from the expansion had not yet caught up to the demand for good pitching.

Well, as it turns out, the ball might be "juiced".  A recent article in Discover highlighted a study by Dennis Hilliard, director of the crime lab at the University of Rhode Island.  Hilliard and 5 colleagues gathered balls from 1963, 1970, 1989, 1995, and 2000. They cut through the outer layers of the balls and tested the cork-and-rubber centers for elasticity.

For those who've never opened as baseball, it is made up of a compressed ball of cork, surrounded by two layers of rubber - one black, one red.  Around this center are three layers of wool winding and one of cotton. This is then sprayed with a coating of rubber cement to prevent it from unraveling.  The final part is the leather covering we are so familiar with, stitched together with exactly 108 stitches of red waxed string.  (BTW, there are exactly the same number of stitches in a baseball as there are beads in a Catholic rosary and a Buddhist mala.  Neat, huh?)

Anyway, Hilliard and crew dropped each of the compressed cork-and-rubber centers from about 15 feet. The three oldest centers bounced an average of 62 inches. The 1995 and 2000 balls bounced an average of 82 inches— about 30 percent higher.  However, that's not necessarily conclusive, as cork begins to lose elasticity after about 10 years.  Anyone who's ever had a fishing rod with a cork handle can attest to that.

So they tested the yarn windings.  And here is where they hit the jackpot.  The older balls' yarn was made almost entirely of pure wool.  As the balls got younger, the amount of synthetic fibers increased.  Major League rules state that the yarn can not be more than 15% synthetic.  (yes, MLB has rules for something as tertiary as the yarn... and enforces them about as well as they do the strikezone).  The 2000 ball was more than 20% synthetic.  Why is this significant?  Well, wool absorbs moisture very easily, and the humidity can deaden a ball by relaxing the tension in the winding and reducing the elasticity of its fibers.  Polyester and nylon, two of the most common synthetic materials used in yarns, are entirely resistant to moisture.  So balls made with more synthetic materials are more elastic and would travel farther from the same bat impact as ones with more wool.

So between the possibility of a more elastic center and the evidence of more elastic winding, it's almost certain that the ball is playing a role in the home run explosion.  Early indications are that the dates this research offers places the balls coming into the league at roughly the same time as the home runs started to pick up.  Obviously more testing needs to be done, especially with regard to exactly when more synthetic materials were used and how much humidity affects the flight of a "wool ball" as opposed to a "synthetic ball".  However, it's looking more and more like those old timers were right: the ball IS juiced.
 

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