Answer:
I am used to bat with, yet I never get a hit. I am near a ball, yet never thrown. What am I?
You use a knife to slice my head and weep beside me when I am dead.
I am a shimmering field that reaches far. Yet I have no tracks and am crossed without paths.
In the sun I like to play; in the rain I goes away; walk or run I always follow; in the mud I always wallow.
You find me behind the stars; or in a sixth seventh or third. It takes something round a computer and me to make pie. I am bigger than anything you can think of.
As round as an apple. As deep as a cup. All the king's horses can't pull it up.