Question

Is the sentence the leaves danced across the yard is simile or metaphor

Answer 1

It's a metaphor. 

To help you understand why, here's the definitions of both:

Simile: it's a figure of speech involving the comparison of one thing with another thing of a different kind, it's used to make writing seem more vivid.

Metaphor: this is also a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.

Answer 2

This is a metaphor because simile uses like or as in a sentence.