The conflict between J.T. Yorke and Nic began in Season 6 when the Degrassi vs Lakehurst war started. 

Conflict History

Season 6

In Can't Hardly Wait, after Nic insults his ex girlfriend Mia at a basketball game in front of everybody, she slaps him which then starts a fight between the students of Degrassi and Lakehurst. J.T. hits Nic with his mascot head. Then as J.T. and Toby are walking from school, Nic and his friends confront them. He calls them "Degrassi Nerds" and tells them it isn't over.

In What's It Feel Like to Be a Ghost? (2), Nic blames J.T. for starting the fight from the basketball game. However, Mia thinks that Nic is just jealous that she and J.T. are dating. Later, J.T. goes to Lakehurst and confronts Nic. J.T. tells Nic that he's just jealous that he and Mia are dating. But Nic says that he doesn't care about Mia and that she's just a dumb slut. He then decides to fight J.T. with his friends and J.T. agrees. However, Mia stops him and tells him that he's better than Nic and not to go down to his level.