Which of the following devices is used to test a sport field for hardness?

The Clegg hammer is a device specifically designed to test the hardness of sports fields, particularly when assessing the suitability of surfaces for athletic activities. It operates by dropping a weight from a fixed height onto the surface and measuring the deceleration upon impact. The results indicate the hardness of the surface, which is crucial for ensuring player safety and performance. A more rigid surface can lead to increased risk of injuries, while surfaces that are too soft may not provide adequate support.

In contrast, a soil probe is generally used to collect soil samples or assess soil density rather than measuring hardness. A pocket penetrometer measures the resistance of soil to penetration, which is more indicative of soil texture and compaction but does not provide a direct measurement of hardness as related to sports fields. A moisture meter, while useful for determining the water content in soil and its potential effects on surface conditions, does not assess hardness directly. Therefore, the Clegg hammer is the appropriate tool for evaluating the hardness of sports fields.