Derrick Walker is too used to handling difficult roles. He succeeded former Kansas State star and current New England Patriots backup Michael Bishop as quarterback at Blinn ( Texas) Junior College. He then moved to Iowa State, where he was relegated to backup duties behind Sage Rosenfels. Last fall Walker completed 9 of 18 passes for 106 yards and threw two interceptions. He seemed unlikely to see much more action than that this year as a senior, so during the off-season he volunteered to play outside linebacker. The switch has paid off for the 6'2", 220-pound Walker, who has made 40 tackles, including two sacks, broken up three passes and forced and recovered a fumble. He has become a cornerstone of a defense that has helped carry the Cyclones to a 5-1 record. If Walker, who is married with two daughters, ever needs to explain to his kids the importance of taking on challenges, he can tell them about his senior season.