Giannis Antetokounmpo is reminding us all why his nickname is the "Greek Freak" ... 'cause the NBA superstar took his first boxing lesson Thursday -- and it was pretty freakin' scary.
The 6-foot-11 Bucks forward -- lookin' as jacked as ever -- learned how to throw some jabs and hooks ... and the video is wild.
His trainer looks tiny ... and when G throws the haymakers -- there's some hold-your-breath moments.
FYI -- Antetokounmpo ain't the first gigantic NBA player to lace up the boxing gloves ... Shaq actually fought Oscar De La Hoya back in 2009.
Funniest part ... Giannis captioned the vid with "StayFreaky"
The LeBron-less Eastern Conference has officially been put on notice.