Hammer time: management practices and field surface hardness

As sports field managers, you take pride in your field and want it to be not only beautiful but be safe for all involved. Athlete safety should be the number one priority of a turfgrass manager in any capacity. Injury in the form of concussions have been a concern in the past, but is gaining more and more attention on a national level from concerned parents and athletes, the media, and various research organizations.

While most concussions may happen from athlete to athlete contact much of the previous research has been on making the game safer as well as improving helmets and equipment, but surfaces are also to blame. According to the American Journal of Sports Medicine, approximately 10-15%, up to 20% at times, of concussions in American football are caused by head-to-surface contact. Increased surface hardness results in a higher likelihood of concussions.

Recently, the NFL began requiring more action in the realm of field maintenance and documentation of field maintenance practices, which should result in a safer playing surface. Not only were they concerned with helmets, cleats, and pads and how they could better protect the players, but also they began to be concerned with field surface hardness (FSH). The NFL now requires each field manager, whether a natural or synthetic surface, to perform field surface hardness testing 72 hours before every game using a certain set of protocols.

Surface hardness is tested with a Clegg Impact Tester by dropping a weight (2.5 kg hammer) from a fixed height onto the playing surface, an accelerometer in the missile will then give a value of how quickly deceleration took place. The resulting value is referred to as the Gmax. The Clegg Impact Tester must generate a value of 100 or less to pass NFL guidelines; if the level is found to be over 100, action must be taken to alleviate the surface hardness before the game is played. This could include performing additional cultural practices and moisture management on natural surfaces and the addition of crumb rubber and proper grooming of a synthetic surface. The NFL is the highest level of play in American football, so if they are concerned with field maintenance and resulting safety why aren’t lower levels of play? This evaluation was conducted at the NCAA Division 1 level of play, which includes a high standard of maintenance similar to the NFL.

Over the 2016 football season, field surface hardness was evaluated at Iowa State University (ISU) and the University of Oklahoma (OU) to survey the impact of management practices on FSH from game to game. Both study sites have sand-based football fields with ‘Rush,’ ‘Midnight,’ ‘NuGlade,’ and ‘Everglade’ Kentucky bluegrass originally sodded in 2008 at ISU and ‘Latitude 36’ bermudagrass sodded in 2014 at OU. Thirty-two locations were tested on each field 24 hours before each home game was played (a total of six home games were played on both fields), with the goal of accounting for differences in wear across the field and management as was found by Rogers and Waddington, 1990. Another goal was to investigate if painted areas on the field had higher surface hardness values than non-painted areas. These locations were derived from the NFL testing protocol; the locations outlined in the ASTM 1936 Standard, and other locations being added for additional test points. Both FSH and a Field Scout TDR Probe for volumetric water content (VWC) were sampled with 3 subsamples at every location.

After data was collected, a statistical analysis was run in order to separate locations and to correlate FSH and VWC. Each study site analyzed separately due to significant differences between locations. At no point during the study did any test location at either University have a surface hardness value above 100. At each study site, FSH did increase over the season from Game 1 to Game 6. Locations 13, 20, and 21 proved to be significantly harder than other test locations on most testing dates during this study. These points were all locations of heavy foot traffic, which would result in higher compaction. Field surface hardness and VWC did not have a strong correlation at either location; this is most likely due to few differences between VWC throughout the evaluation period. More data is needed to determine if athletic field logos and repeated painting will increase the surface hardness of athletic fields. Water management, having a sand-based rootzone, along with cultural practices are important aspects of field surface hardness. Both the University of Oklahoma and Iowa State University performed solid tine aerification after each home game, which helps relieve surface compaction.

Whether natural or synthetic turf, field management practices directly affect field hardness and, in turn, risk of head injury. A properly maintained playing surface can help reduce head and general player injury risk. Research should continue to be done in relation to FSH and VWC on all types of playing surfaces with different soil types, usage rates, and different management practices. Previous work by Rogers and Waddington, 1990, reported differences with management levels, soil types, and turf cover. Even high profile fields have increasing FSH numbers throughout the season when tested right before a game, therefore more testing is needed across all levels of play. More research is needed to determine at what surface hardness is most likely to result in a head-injury, and if that can be detected using the Clegg Impact Tester. This was strictly an evaluation and not a controlled study. The overall goal of this evaluation was to show a greater need for surface testing across all levels of play in not only football, but all other sports involving a natural or synthetic turf field.

Chrissie Segars, PhD, is assistant professor of plant and soil science, University of Tennessee at Martin, Adam Thoms, PhD, is assistant professor and Extension turfgrass specialist at Iowa State; Tim VanLoo, CSFM, is Manager of Athletics Turf/Grounds at Iowa State; and Jeff Salmond, CSFM, is director of athletic fields at the University of Oklahoma.