I generally wear a M size but decided to order the S size and it was a wise choice.  This short is a fleece-like material inside, a little warm, and snug in the small size for wearing them playing tennis- the small size gives a little support, and the stretch in the material is enough so that having 2 tennis balls in my pocket doesn't cause any binding restriction of movement.
They are also good for just lounging around in - the two front pockets are generous and I can easily carry my keys, and phone without fear of them falling out.  The back pocket is equally sized and the snap ensures that when I have my wallet with me it will remain secure.
I have washed them before wearing and the shrinkage is minimal- the blend of material doesn't dry very quickly but even hang drying the fabric stays soft.