Thought this might interest some of you. A Popular Mechanics story a couple of years back described how the type of football field surface is measured in terms of shock absorbency by dropping an object the size of a human head and neck (20 square inches and 20 pounds) from 2 feet above the respective surface. The metric is called G-Max. A low G-Max absorbs more energy than a player. Grass has a G-Max of 60, while synthetic turf has a G-Max of 120. The hardest surface is frozen grass. Most people associate high g-forces with fighter pilots or astronauts. But few things can match the g-load of a vicious football hit.