This is core aeration.

In the fall we remove material from the greens for a couple of reasons. One of the reasons we do this is because we need the best possible drainage throughout the fall to the spring. Another reason we do it is because we want to get as much air and nutrients into the soil for the rainy seasons. There is quite a bit more work with taking a core but it also helps remove organic material. We have to harvest the cores with a harvester and clean the greens before we sand. It takes a lot more effort and time and they heal a little slower. They heal slower because the sod was removed and the grass has to grow all the way over the hole. Since the sod does not return to its original location it allows nutrients and air to enter a lot longer.