Luis Castillo is so sure he'll never take steroids again that he'll back it up with his bank account.
The Northwestern defensive tackle was chosen by the San Diego Chargers with the 28th pick, two months after testing positive for androstenedione, labeled a steroid by the league.
Castillo said he made "a huge mistake" in taking the drug to help his performance at the scouting combine in February after his injured elbow was slow to heal.
"I'm willing to put in my contract I'll never test positive for anything again," Castillo said. "If I do, I'll return my entire signing bonus. . . . I've never needed that to play football. . . . I made a one-time mistake which will never happen again."