Kerala was one of the most caste-divided states in India before the British.
The challenge: put a farmer on the throne.
Look, the caste system varied hugelu over time. Which time period are you talking about?
The entrenched 17-18th C version actually originated from the fact that the Nair warrior clans (who themselves had large farmholdings) managed to sieze local power independent of royal authority. Also the Britishhad nothing to do with breaking caste strictuire (their administration tended tomactually entrench a simplified form of the caste system across India). When the Maharajas of Travancore established dominance over the entire region they began to break down the caste restrictions as a means of centralizing royal authority and reducing the power of the Nair clans.
The Nairs themselves (going by their customs) may actually have what might have been considered as low caste tribal origins bit started their rise to power hundreds of years earlier through alliances with the newly arrived Namboothiri Brahmin caste against the Buddhists and Jains who were stll prevalent in Kerala.
So I could fulfil your POD by saying that in 1100 a Nair farmer who is also a clan head helps lead a pogrom against the Buddhists and at the end of it finds himself on the throne of Calicut