Sorry I didn't see it, I spend alot of time in this forum and you should have posted anemone and clownfish questions here first. I do a search now and again for anemone questions and try to move them all here, I just missed yours.
Now. I would like to know what type of anemone we are talking about, also what type of clownfish.
Why was the clownfish hiding? Was there something that it was afraid of, or stressed about? Water paramiters, preditors? How long have you had the clown and the anemone?
Can you move the rocks and find a way to help the clown.
You might try pointing a powerhead at the anemone in order to get him to move.
Give me some answers and we will form a plan of attack. or try the powerhead method asap if you think the clown is in danger.
Thomas