INFIELDS

By Evan C . Mascitti and Andy McNitt , Ph . D .

A baseball often touches two different surfaces during the same play . This sets baseball apart from other ball sports . Most ground balls take their first bounce on the turf and are fielded on the infield skin ( see Figure 1 ). The concentration of play in this small area means that infield playability consumes much of the grounds crew ’ s focus . Experienced managers know instinctively when the ball is reacting the way they want , and they can produce a consistent surface despite changing weather conditions . Playability can be an ambiguous term , because it is easy to observe but hard to describe .

This article unpacks infield playability by combining practical observations with bite-size pieces of physics . We will cover the following ideas :

1 . Consistency is king 2 . Components of speed 3 . Corkboard = plasticity + stiffness

CONSISTENCY IS KING Above all else , infielders want a consistent , predictable surface . This means no surprises about how the ball will react from one hop to the next , and that the field will play identically throughout a game and over the season . Elite athletes can field almost any ball — fast or slow — so long as the bounces are the same each and every time . Infielders prefer ground balls to “ hug ” the surface : a shallow path makes the ball easier to track and collect . The grass and dirt areas should have similar speed , and the transition between them should be seamless .

Predictability is crucial for players to be able to do their jobs . If the final hop is deflected by just a few degrees , the ball can easily carom off the heel of a player ’ s glove or scoot beyond his reach .

COMPONENTS OF SPEED Players and coaches sometimes ask us to “ speed up ” or “ slow down ” the infield , usually by adjusting the cutting height of the turf . Ball response is more nuanced than fast vs . slow , and canopy height plays only a minor role . However , it has been said that perception is reality , so a perceived change may satisfy such a request — even if we fib about having lowered the reels by 1 / 8 inch or so . Ball response is divisible into three important elements : pace , bounce , and spin .

Pace Pace is the relative velocity of a ball after impact . Infield pace is mostly determined by hardness and friction . It is measured as a simple ratio , the Coefficient of Restitution ( COR ):

Figure 1 : Most action occurs on the infield skin .

There is limited research on infield pace , but data suggest that soil properties affect COR more than cutting height or thatch . Jim Brosnan , Ph . D ., measured COR on real infields and on research plots ( Brosnan and McNitt , 2008a ; b ; 2011 ). Infield COR ranged from 0.4 to 0.6 , meaning a ball retained 40 % to 60 % of its initial velocity after the first bounce . COR was generally higher on skinned surfaces than synthetic turf , which had a similar ( but slightly higher ) COR than natural grass .

In the work by Dr . Brosnan , pace was closely related to surface hardness . Hardness is easy to measure with the familiar Clegg hammer or the F-355 device ( for

22 SportsField Management | March 2021 sportsfieldmanagementonline . com