I do not know what the format is.
But, based on the information on the score card picture that you posted, it appears that the following is the way it works:
After "Stage 1", the bottom 3 in the rankings were forced to shoot in the "Eliminator 1 shotgun". The winner of that eliminator stage, and the top 3 from Stage 1 got to stay and compete in "Stage 2". Now the Bottom 2 in ranking after "Stage 2" must compete in "Eliminator 2".
Based on this I would guess that the winner of "Eliminator 2" and the top 2 from "Stage 2" will then compete in "Stage 3", Then the Bottom 2 in ranking after "Stage 3" would compete in "Eliminator 3" with the winner of "Eliminator 3" returning to compete against the winner of "Stage 3" in "Stage 4" for the championship.