Links between ground conditions and injury – Part 1

Written by:

Phillip Ford
PhD candidate, University of Ballarat
September, 2013

Part one of four

For several years, the University of Ballarat has been investigating the links between ground conditions and injury in football. I live in Ballarat, and when I finished a long career as a teacher of turf management in 2008, I was fortunate enough to be taken on at UB as a PhD student to study the effects of agronomic (soil and plant) factors on ground hardness and traction, and the implications for ground-related injury.

Apart from the more obvious problems (e.g. glass, rocks, holes, unsafe fences etc.), the two main factors linked to non-contact, ground-related injury in football are hardness and rotational traction. Excessive hardness is mainly linked to bruising, fracture and concussion, and excessive rotational traction has been linked to ankle and knee injury, especially anterior cruciate ligament (ACL) injury.

To cut a long story short, my research demonstrated that the safest football ground, from both a hardness and a traction point of view, was a surface with full grass coverage across the whole ground. I should rename my thesis: “Football ground safety – the bleeding obvious”.

But it’s not as obvious as it seems. Have a look at community-level football grounds at this end of the season. A lot of them are completely denuded of grass in the high-wear zones. This is accepted as normal and inevitable, but my research showed these denuded areas are where player safety is most compromised. Ground authorities need to do more to prevent this denudation by selecting the best grass species, managing traffic, and allocating sufficient money and resources to sustain this full grasscover. This is particularly problematic when water restrictions are in force.


When I started my research, Australia was in the grip of the 1997-2009 “Millennium Drought”. Water restrictions on community-level grounds had led to the loss of turfcover on perennial ryegrass grounds, leaving them largely bare (see Figures 1 and 2) and unacceptably hard. Testing of council grounds in Melbourne by Michael Robinson, from Sportsturf Consultants, found that more than 25% of these grounds had Clegg Hammer hardness values greater than 200 gravities at the start of the 2007 and 2008 seasons, with values on some grounds reaching nearly 400g. Many councils (and their insurers) adopted a threshold of 120g for safe play, and as a consequence many community-level grounds were closed.

Figure 1: Community-level, unirrigated Australian football field in Ballarat, December, 2009. Perennial ryegrass coverage has been devastated by drought, but a natural invasion of couchgrass in the goalsquare area is surviving well, as shown below in Figure 2.

The 120g Clegg threshold was largely based on research at Melbourne University by Dr. Ian Chivers and Dr. David Aldous, who assessed players’ perceptions of hardness in elite-level football. The applicability of this research to ground-related injury in community-level football is questionable. In Queensland, research by Keith McAuliffe and Matt Roche concluded that Clegg values for community-level football grounds above 150g were “cause for concern”, and that the absolute upper limit for play should be set at 200g (McAuliffe & Roche, 2009). The American standard (ASTM F1702-96) doesn’t set any Clegg threshold at all for natural turf. The question of a sensible upper threshold for football is critical, but as yet the medical evidence has not provided sufficient guidance on what it should be.

A recent meta-analysis of football injury studies by Petrass and Twomey (2012) concluded that there was an apparent risk of increased injury on harder/drier grounds, but that good quality evidence was lacking. Such evidence is susceptible to ‘confounding’ factors. For example, harder, drier grounds allow faster running, which on its own could contribute to more injuries. Several of these studies found an ‘early season bias’ of higher injury rates early in the season, which could be attributed to harder/drier grounds – but they could also be attributed to lack of fitness, or ‘attrition’, where injury-prone p0layers suffer their injury and are removed from the player population for a long period. Remember, too, that nearly all of these studies are undertaken in elite or semi-elite football, not community-level or junior football.

The most rigorous and direct injury study in community-level football was conducted by Twomey and colleagues (2012), involving 40 teams in Ballarat and in Western Australia during 2007 and 2008 (Twomey et al., 2012). They measured Clegg hardness over two seasons at nine locations on 20 grounds, and also recorded the nature, cause and location of injuries. Hardness levels through the study varied between 25 – 301g. A total of 402 injuries were recorded and for 352 of those the exact ground location of the incident was known, to allow matching with Clegg values. Only thirteen of those 352 injuries occurred on ground locations where hardness exceeded 120 g. Eight of those thirteen were player-contact injuries, so there were only five ground-related injuries on areas where Clegg values exceeded 120 g. And none of those five ground-related injuries was a concussion or a fracture. In fact, the severity of injuries on hard grounds was actually lower than on soft grounds.

To conclude this section, there is no convincing evidence that dry, firm, hard surfaces contribute to higher ground-related, non-contact injuries in football. And there is no objective evidence on what the Clegg upper threshold should be for football grounds. This requires further research, but I agree with McAuliffe and Roche that a more realistic cause for concern for community-level football is around 150-160g.