Who were the Shanars? What happened to Shanar women when they defied the local customs?

Hint: Shanars, which now are known as Nadar, are the lower caste people who were known to have worked in the palmyra industry where they used to cultivate and climb the palmyra palm, and then they would boil its juice to form coarse sugar. Apart from this, they were also involved in the toddy trade.

 Complete answer:
In the 19th century, the shanars used to work under the upper-class Nair community as a subordinate class after migrating to south Travancore. It consisted of people from different lower caste stature and hence, formed a single caste which is known as Nadar as of now. The shanars were a part of a rigid hierarchy that was under the strict control of Nairs which led them to face extreme forms of casteism. They were banned from using umbrellas, they were not allowed to wear slippers, and on the extreme end, exposing one’s upper body (both male and female) was considered respectful towards the upper-class people. These rules and regulations were so rigid that the banishment of the same led to violent punishments. So, this casteism forced the lower-caste people to follow strict codes of lifestyle where they were in full control of the Nairs for what they could eat, wear, etc.
In the early 1800s, the shanar women got influenced by the Christian community and started adopting Christianity whose basis is the equality of both men and women and under this influence, they started abandoning the code of having a bare chest in front of the high stature people. They started campaigns for the Nairs to repeal the dress code and ignored their orders. They wanted to be dressed like upper-class women and wanted to cover their upper body the same way as them. Hence, they would their upper body and denied offering free labor to the Nair community which led upper-caste people to attack them and hurt them by tearing their clothes apart.

Note: Till the early 1900s, tax collectors used to visit the house of lower-caste and untouchable women to collect Breast Tax from them since the age they have hit puberty and started developing breasts. The tax was evaluated on the basis of the size of their breasts.