As per Thiruvaimozhi by Nammazhvar, Lord Krishna married Nappinnai (Neeladevi ) after bravely taming seven bulls through the act of Jallikkattu.
Neeladevi took the avatar of Nappinnai as the daughter of Yasodha's brother Kumbha. Sridevi, Bhoodevi, and Neeladevi are believed to be the wives of Lord Vishnu. Neeladevi is to Krishna avatar as Bhoodevi is to Varaha avatar and Sridevi is to Rama avatar.
So, we understand that from Dwapara yuga (Lord Krishna’s period), taming the bulls has been in practice as a display of one's valour. Today, we call it Jallikkattu, which is a competition that showcases one's bravery by taming the bulls.
Here is the mythological reference about Jallikkattu in Thiruvaimozhi by Nammazhvar:
thOLi sEr pinnai poruttu erudhEzh thazheeik
kOLiyAr kOvalanAr kudak kUththanAr
thAL iNai mEl aNi thaN am thuzhAy enRE
nALu nAL naiginRadhAl endhan mAdharE
Here “erudhu Ezh thazheeik kOLiyAr” refers to– One who embraced the seven bulls.
Nammazhvar is the fifth saint among 12 Alvars who contributed to Nalayira Divya Prabandham. He remained speechless right from his birth and got enlightened by Madhurakavi Alvar. He has been given special honour in Vaishnava temples and Araiyar Sevai in Srirangam temple is dedicated to him. His verses amount to 1352 among the 4000 verses and his Thiruvaimozhi is famous for the description of Lord Vishnu, which is dipped in piety.
In Tamil, Nalayiram means 4000. Nalayira Divya Prabandham is a collection of 4000 Tamil verses recited by 12 Alvars and was compiled by Nathamuni during the 9th & 10th centuries. These verses have been considered as the Tamil Veda by Vaishnavites. The verses of Divya Prabandham, describing the avatars of Lord Vishnu, are recited in Vaishnava temples on all special occasions. Divya Prabandham is recited in marriages as well.