(TMZ) The biggest hit at the World Series came AFTER the game -- when an Indians fan KO'd a Cubs fan right outside the stadium ... and the whole thing was caught on video.
The two men had been arguing in the street outside Progressive Field in Cleveland when the Indians fan -- in a "Cleveland Against the World" shirt -- threw a haymaker right hook ... knocking the Cubs guy out cold.
TMZ Sports has learned the victim was 36 and did get transported to a hospital in stable condition. He suffered a cut to his mouth and a head injury. He did regain consciousness and told police and paramedics he'd been in an argument that got physical.
He told police he did not want to file a report and even refused medical treatment, initially ... before reluctantly agreeing to be transported.
TMZ spoke with Chris Vallimont ... who says he pulled out his phone and started to record after he saw the two men cussing at each other right outside Progressive Field.
"The Cubs fan said, 'You guys just blew a 3-1 lead, f**k you.'"
The Indians fan shot back, "Fight me, p****."
The Cubs fan replied, "Hit me now, I dare you."
The Indians fan accepted the challenge and blasted the Cubs fan in the face -- and then immediately fled from the scene while the Cubs fan laid on the ground unconscious ... so says Vallimont.
"He probably didn't move for about 12 minutes."