"He heard there may be a fight or scuffle," said Vernon.
Vernon said after class, his son and more than 50 others walked across the street to see what was going on.
"Basically, one guy punched another guy," said Vernon.
Vernon told 10News his son saw two people he didn't know fighting, which quickly turned into a free-for-all.
10News learned Vernon's son, a basketball player at Crawford High, saw one of his teammates get caught up in it and tried to pull his friend out.
He did, but soon after, he looked down and saw the blood -- Vernon's son had been stabbed in his left leg.
"The knife went completely in as far as it could go; at least several inches," said Vernon.
Vernon's son was among four students stabbed in the melee. He said the fight came in the wake of three other fights outside the school the week before and constant chatter on social media.
Attorney Dan Gilleon, who represents the families of three injured students, just filed a claim against the San Diego Unified School District, alleging negligent supervision.
"They simply ignored all indications there would be a fight, and they allowed these kids to get together and hurt each other. Anybody they see as an authority figure probably could have prevented this, and they were simply absent," said Gilleon.
Vernon said his son's wound has healed but there is still muscle weakness.
An SD Unified spokesperson declined to comment, citing pending litigation.