Even after 16 years, memories of Steve Young’s first known concussion on a football field are as vivid to one witness as memories of the one suffered by the 49ers quarterback last month.

“He could barely make it off the field,” said Robbie Bosco, who temporarily replaced Young as Brigham Young University’s quarterback in a 1983 game against Utah State. “He needed help to get to the sidelines.”

At the time, no one could know that this concussion would be the start of a string of at least eight during Young’s career, a series of head injuries that threatens to make his Sept. 27 game against the Arizona Cardinals his last.