He could a be 2-3rd generation game back cross. It'll make sense with his appearance.I hatched him and I didnt start with any pure gamecocks. He could be 1/8 though. I don't know what generation he is.
male 1/2 Orpington 1/2 American game
female 1 American game
offspring 1/4 orpington 3/4 game
If I had a fertile male in that group, it could have bred back to the original female and given 1/8 orpington 7/8 game
I'm trying to recall if I had any cock(rell)s around