Japanese phrase meaning "Go for it"! or "Do your best!" Similar to how English speakers say "Break a leg!" It's usually echoed before major events involving competition.
Commentator A: It is the finals round of our matchup with our two competitors in their respective corners!!
Crowd: Gambatte!!
Fighter A: what are they saying ?
Fighter B: They are cheering us on. They're telling us to "Do your best!" or "Break a leg!"
"That guy has a big Gamnat"
"Gamnat haircut"
"Sup Gamnat"
"Man, that shit is gamnizzle"
"Gaminator"
"Get off my Gamnat"
"Im going to bust your Gamnat open if you don't shut up."