A player was prematurely celebrating winning the match when he accidentally knocked the ball over the crossbar in the dying seconds of the game.
It meant Hawick Youth threw away their two point lead and the under-18s clash with Gala Wanderers ended in a draw.
Match referee Malcolm Changleng told OceanNewsUK he had never seen a similar incident in 30 years of watching rugby.
A video of the bizarre moment has been viewed more than five million times on X, formerly known as Twitter.
Mr Changleng said Hawick were ahead in the Borders Semi Junior League match on Saturday when Gala scored a try.
It meant the home team had one final chance to seal a draw with a conversion attempt.
But the kick fell short and as Hawick ran to celebrate the win, their scrum-half accidentally knocked the ball over the post.
The referee awarded the conversion to Gala before blowing the final whistle and ending the match with the score tied at 33-33.
"I've been refereeing rugby for over 30 years and I've watched an awful lot of rugby and I've never seen this before."
He said it was made in the "last play of the game".
The referee added: "Rory from Gala kicked the ball and it went stotting through the air but it didn't quite make the post.
"But as Hawick are running out to cheer a win in the local derby, their number nine kicked the ball - it hadn't hit the ground - and it went wellying over the post."
'Technically an own goal'
Although the Hawick scrum-half knocked the ball over the post accidentally, a lesser-known rugby law meant that the conversion still counted.
The rule states that if the opposition team touches the ball during a conversion and the kick is successful, the goal stands.
"I went into time out and brought the captains and coach across," said Mr Changleng.
"I said that there were over 500 laws in the book, but one of the laws says that if the ball touches a player anywhere and it goes over, it's a conversion.
"You can't get an own try because if you take the ball over the line and dot it down, then the opposition get an attacking scrum.
"But if it goes over your own post and you've kicked it over, I suppose that's technically an own goal."
The referee said that as he blew the whistle for full time, the maroon of Gala were cheering but he saw "the green of Hawick just slink to the ground".
Mr Changleng added: "They were ahead for most of the game, five tries apiece, a very good game, so I think they thought they had won it.
