#4 Yoshi-Hashi
Yoshi-Hashi has a very odd few years, but he has had a few upset victories. In last years G1 Climax he won over Yuji Nagata a former IWGP Heavyweight Champion and G1 winner and Bad Luck Fale, a former IWGP Intercontinental champion, and in 2016 he beat the eventual winner of the Tournament, Kenny Omega a former IWGP JR Heavyweight Champion and also a former IWGP Intercontinental Champion.
So far in this year, Yoshi-Hashi hasn't pulled off an upset singles victory yet, but he has had very good matches against Tetsuya Naito and Kota Ibushi. I believe he will pull off an upset victory in the G1, and he is in the A block with Tanahashi, Hangman Page and EVIL.
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If Yoshi-Hashi does pull off an upset, I believe if anyone it will most likely be against Michael Elgin, as Elgin is an established name in NJPW and a loss against Yoshi-Hashi will help Yoshi-Hashi and will not affect Big Mike all that much.