Which figure of speech is used in this text?
Erin Brockovich, a single mother with no legal training, helped win a daunting court battle against a Goliath energy company.

 - allusion
 - onomatopoeia
The text uses an allusion, a brief reference to someone or something well known.
Goliath alludes to the giant warrior in the Bible who was defeated by a much smaller opponent, David.