“…The aim of this work is twofold: on one hand, to get sharp regularity estimates for solutions to an obstacle type problem involving a degenerate fully nonlinear operator. On the other hand, in order to achieve such purposes, we appeal to the improvement of flatness technique and geometric estimates that have proved to be very useful in dealing with regularity issues for elliptic/parabolic PDEs in the last decade (see, [1], [3], [4], [5], [7], [12], [13], [19] and [26] for some enlightening examples), but that, to the best of the authors' scientific knowledge, have not been applied to free boundary problems of obstacle type as the one dealt with in this paper.…”