Thresh can leave the area from Prize Fight event if it can hook any kind of enemy outside the ring.
This will prevent Thresh from moving any place outside the ring. If he tried to move in direction of inside the ring, Thresh will move until he arrives inside the ring or the player presses "S" to stop champion movement.
1. Pick Thresh in Nexus Blitz
2. Wait for Prize Fight event
3. Once inside the ring, use the "Q1" skill to the Gromp which is below and go to it using the Q2.
4. You shouldnt be able to move until you click within the ring, which makes the character move towards the ring.
4a. You will be able to move freely if you win the duel as Thresh being stuck outside the ring
If by any means you win the duel by being outside the ring, The game will try to teleport within, but youll be outside instead of inside, allowing full movement. If you go to base, youll be healed, meaning that you cant die from burn damage. This can be done each time you win, until the event is won, but each time you win an event, youll be teleported back outside the ring.
Another entities such as Ivern's R, (Daisy) will be able to freely move outside the ring
Those videos were made in 1 vs 1 custom. That doesnt mean that the bug isnt there, but it was the easiest way to reproduce said bug