The figurative language in "she is a beast on that soccer field" is metaphor.
Step-by-step explanation:
Writers use metaphor to compare one object to another and bring out the similarities between them. In the phrase: She is a beast on the soccer field, the subject is being compared to a beast to bring out the similarities of being fast, wild, unpredictable and strong. While mostly the term 'beast' is used to identify the characteristics of being cruel and uncivilized, in the above phrase, it is used to identify the good sportsmen quality of the subject.
There are several figure of speech that people use to make their writing more effective and attractive. They are non-literal in nature. That is, the subject being called a beast does not mean that she is a beast in literal sense. She just have the qualities that are similar to a beast. The use of metaphor allows the listeners/readers to get a better picture of her sportsmen qualities.