Frost occurs on clear cold nights when turfgrass plants re-radiate heat (exothermic reaction). As the plant loses heat to the atmosphere the plant leaf cools. If the plant temperature is cooler than the air temperature then moisture from the atmosphere will condense on the leaf. If the leaf temperature drops below freezing then the water freezes and frost forms. This will occur even if the air temperatures are slightly above freezing. At this time of the year it is not uncommon to have frost form even if the air temperature is in the mid to high 30s. This is due to the fact that the soil temperatures are still creating a much cooler microclimate at ground level. Think of the scenario when you pour your favorite beverage into a glass that has been in the freezer. FROST!
Frost itself does not cause damage, but injury does occur with traffic on frosted areas. Turf damage is generally superficial. This is not to say that traffic should be allowed on frosted turf. If traffic occurs, whether it is foot or mechanical, damage caused by crushing the leaf blade will occur. Initially the symptoms will appear purplish to black in color. The damaged turf will then progress to a straw color. If no damage occurs to the crown (the growing point), recovery will occur from the generation of new leaves. However if the crown of the plant is damaged the plant may be severely damaged or worst case it may die.