Knauf was battling pain in his lower back, which started during track in his senior year at Santa Fe (Fla.) High School. The freshman receiver wanted to play through the pain, but it wouldn't go away.
"It was like a bad ex-girlfriend," Knauf joked on Tuesday.
Inside Purdue's Mollenkopf Center this spring, Knauf is moving at full speed. It was a painful process back to practice field.
Knauf struggled to walk with the pain in his back. It even hurt to sit. Needless to say, the rehabilitation was agonizing, too. Last fall, he spent hours each day working toward recovery. It wasn't until the Boilermakers' bowl preparations when Knauf finally felt able to play, but his redshirt kept him sidelined.
Given the type of injury, Knauf still must work rehab-like treatment in order to prevent a flare up.
"It's something I'll have to work out for the rest of my life," Knauf said. "But I feel good on the field."
Last season, Knauf felt additional pain knowing he wouldn't be on the field with his team. Even as a true freshman, the receiver was poised to have a role in the offense. Instead, he wasn't able to suit up.
Looking at his situation now, Knauf sees his redshirt year as a great gift.
"You have a whole nother year ahead of you to get bigger, faster, stronger and smarter," he said.
The pain still exists and won't go away, but Knauf is back to form. He is currently working at the Z-Receiver spot—a slot role in Purdue's new pro-style offense. His track-star speed has created problems in practice, and has caught the attention of Purdue's new coaching staff.
"He's a guy that has tremendous speed," said Purdue receivers coach Kevin Sherman of Knauf. "He's a guy that can give you a big play. My whole thing with all of these guys is consistency, and B.J. is one of those guys."
Knauf is at full speed and vying for a starting spot. It's the same position he was in last August, just before the pain in his back become too much. Now, he's feeling better than ever.
"Like high school, honestly," he added. "I haven't really played since high school. I came in, got hurt right away in the summer. It's kind of a blessing to come right in and play again."