Cheered when it tried to get rid of its rider (6)

I believe the answer is:

bucked

I'm a little stuck... Click here to teach me more about this clue!

'cheered' is the definition.
Although both the answer and definition are past participle verbs, I don't understand how they can define each other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.