INFIELDS
Figure 2 : Surface hardness on baseball infields generally exceeds values recommended for American football .
synthetic infields ). Brosnan and McNitt ( 2008a ) found that most infield skins had Clegg values well over 100 Gmax — much higher than values recommended for turf areas ( see Figure 2 ). However , it is worth noting that some fields in this study were substantially drier than typical game moisture . In a baseball context , hardness may be more useful for managing playability than safety , as baseball players are never tackled and rarely become injured by falling on the surface .
Ball-to-surface friction is determined by soil texture , presence of conditioner , and the all-important water content ( Goodall et al ., 2005 ). A thick conditioner layer reduces surface friction because the granules rotate like ball bearings as the ball shears against them . The ball will skid rather than checking up . Friction also affects the ball ’ s release angle , which , in turn , alters the bounce height ( Figure 3 ). that umpires ’ perception of speed was more closely linked to the ball ’ s rebound height than its velocity . A higher bounce means the ball carries farther between bounces , leading to the perception of a faster surface .
Any debate about whether a perceived faster surface really has a greater pace or a greater bounce is purely scholastic , because the players ’ experience is what ultimately matters . Bounce is related to hardness , and a harder surface will appear faster , even if only due to its higher bounce .
Spin The influence of ball spin can be large or small , depending on the ball-to-surface friction coefficient μ ( Daish , 1972 ). If μ is large , the ball “ rolls ” during impact and its
new spin rate is determined by the original incoming velocity . If μ is small , the ball retains some spin as it skids through impact and its release angle is steeper ( see Figure 3 , bottom panel ). The latter is the usual case on closely mown turfgrass .
You can observe this phenomenon during batting practice . It ’ s hard to hit accurate fungoes with full effort , so experienced coaches prefer a flatter but more controlled trajectory with some backspin . The steeper release angle helps compensate for lost velocity by increasing the ball ’ s carry after its first bounce .
It ’ s unusual for a ground ball to be hit with backspin during a game . Most ground balls have forward spin and release at an angle beneath their incoming trajectory ( see Figure 3 , top panel ).
CORKBOARD = PLASTICITY + STIFFNESS We associate the word plastic with man-made products such as disposable water bottles , but the word is actually derived from plastikos , an ancient Greek term for clay . Plastikos roughly translates to “ fit for shaping .” Plasticity is perhaps the most useful property of clay : it helps potters to mold clay into useful objects before firing , and it allows a groundskeeper to scarify , shave and pack soil with proper moisture . New grounds interns are quickly taught the sacred importance of moisture management .
Plasticity is important for two reasons . First , it means the soil will
Bounce The term “ bounce ” defines the vertical rebound of a ball after impact . Some research on cricket pitches suggests that the ball “ speed ” experienced by a real athlete is more related to bounce than pace . Adams et al . ( 2005 ) found
Figure 3 : If the ball can skid through impact , initial spin will influence the release angle . Adapted from Daish , 1972 . sportsfieldmanagementonline . com March 2021 | SportsField Management
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