Indoor courts generally give you a nice clean backdrop so it's easy to see the ball clearly and judge it early. Some outdoor courts without windscreens have very mixed visuals of varying brightness in wich the path of the ball goess through varying degrees of visibility. Grass, parking lot, sidewalk, varying car colors, trees, flowers, people walking by, buildings, sky, water towers, list can really be endless. Seeing the ball clearly along with early preperation are amonng the factors of getting a clean hit on the ball. I don't know why this is but alot of the indoor facilities have very little grit on the surface. This is not true of all indoor facilities, just might be where I'm located. No wind or some of the other distractions that occur outdoors happen when your playing indoors.