Synthetic turf sports fields are designed to have something between the "blades" of turf to hold them up from the heavy backing through which they're tufted, and also provide more of a cushioning effect during impact. Testing has shown the nature of sports injuries are not as severe on synthetic turf vs natural grass or sod, in a number of categories included for soccer and football applications.
Different manufacturers and installers of synthetic turf fields specify their recommendation, which may include separate or integrated alternating layers of silica and/or SBR granules (recycled tire in-fill) of a particular sieve size specification. Or they may push their own variety of in-fill for whatever benefit it may or may not provide.
If you want and need in-fill, we got your field covered. Let us know what the square footage and desired depth for that area, as well as the granulation spec. These would normally delivering in super sacks, banded to a pallet for transport. For this and all estimates or orders, we would need your zip code, delivery destination description, and confirm there's a forklift for offloading (and installation).