09 March 2014

Science of Baseball: Effect of Playing Surface on Batted Ball Velocity

Effects of Surface Conditions on Baseball Playing Surface Pace
Brosnan et al. 2011
Journal of Testing and Evaluation, Vol. 39, No. 3
The speed at which a baseball travels after impact with a playing surface has been referred to as playing surface pace. Little information is available regarding the effects of varying construction and maintenance practices on the pace of baseball playing surfaces. Research was conducted to evaluate the effects of construction and maintenance practices on a non-turfed basepath, Kentucky bluegrass (Poa pratensis L.) turf, and six synthetic turf surfaces. Factors evaluated on the non-turfed basepath included soil compaction at installation, surface scarification, and topdressing with a soil conditioner (calcined clay).The effects of cutting height and thatch thickness were evaluated on Kentucky bluegrass, while the effects of simulated traffic and grooming were evaluated on synthetic turf. On the non-turfed basepath, increasing soil compaction yielded increases in surface pace. Calcined clay topdressing and increasing scarification depth did not affect surface pace. On Kentucky bluegrass, varying cutting height and thatch thickness levels had no effect on surface pace. On synthetic turf, increases in simulated traffic resulted in slight increases in pace. Surface pace measurements on synthetic turf were less variable than those made on natural turfgrass.The results indicate that the pace of commonly used baseball playing surfaces is not easily altered with minimally invasive maintenance procedures and should be addressed at construction or during aggressive renovations.
That abstract might be a bit difficult to parse through.  The link to the pdf of the paper above may also be somewhat problematic.  Really, the take home of this research was that the study evaluated many ways in which the velocity of a 100 mph baseball could differ.  They evaluated three different kinds of turf: Kentucky blue grass, synthetic turfs, and turf-less plots.  None, in this series of experiments, appeared to significantly impact the mean surface pace of the ball.  Surface pace refers to the ratios of the velocity of the ball after striking the ground to the velocity of the ball before striking the ground.  As expected, energy is lost by striking the ground, so all speeds are lower leaving the strike area than they are entering the strike area.  Anyway, ground cover appeared to have no impact on velocity loss.

Grass thickness was also evaluated and yielded no significantly different results.  The heights of the grass evaluated in this study also did not impact velocity loss.  One can imagine though that a wider variety of grass height would eventually produce significant differences, but those differences may only be real at extremes unlikely to be seen at an actual field.  Surface scarification and application of clay top dressing appeared to not affect things either.

Of the variables they did explore, only surface compaction significantly affected velocity loss.  It is difficult to figure out the degree to which this is true because they apparently only repeated the experiment twice, which prevents many different types of statistical evaluations.

Surface Pace
Compaction T1 T2
High 0.543 0.589
Medium 0.525 0.573
Low 0.442 0.527
What the above data suggests is that turf managers would have a hard time affecting how a ball travels.  In other words, the only meaningful way to impact a batted ball on the bounce would be at the time of construction of the field or a rather intensive reconditioning of the playing field.  Certainly some variables were not explored in this paper.  For instance, long grass that is wetted might actually significantly impact surface pace, but that was not explored in this paper.  Additionally, stories we have all heard back in the day about rather clever groundskeepers may have been possible then and not now due to more stringent expectations about playing field conditions.

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