Zion Williamson's incredible athletic feats don't end on the hardwood ... 'cause the hoops phenom smashed a 400 foot home run and threw a football 70 yards -- as a 16-year-old high school student!!!
Lee Sartor -- Zion's basketball coach of 4 years at the Spartanburg Day School in South Carolina -- told TMZ Sports about some of the ridiculously amazing stuff he's personally witnessed.
First up, football.
Remember that video where Zion airs out the pigskin ... launching it into the air?
Well, Coach Sartor -- now the head coach at Erskine College in S.