What are the figure of speech in sentence The boy had butterflies his stomach when he stepped up to bat?

The figure of speech used in the sentence "The boy had butterflies in his stomach when he stepped up to bat" is a metaphor.

Here's why:

* Metaphor: A metaphor directly compares two unlike things without using words like "like" or "as".

* In this case: "Butterflies" are being compared to the feeling of nervousness the boy is experiencing. The boy doesn't actually have butterflies in his stomach, but the comparison helps us understand the intense feeling of anxiety he's feeling.