Current: Brad Davison at Wisconsin. I hate that guy. It sucks I have to watch him for another year.
Past: There's so many, but my first thought was Rocky Calmus a LB for Oklahoma in the late 90s and into 2000. One of my favorite Huskers ever is DeJuan Groce. During that legendary NU vs OU game in Lincoln Groce returned a punt, was tackled by Calmus. While on the ground Calmus was twisting Groce's ankle to the point you could see Groce was in pain and he threw the ball at Calmus. Which of course was flagged for a 15 yard penalty. It was clear as day what that bastard was doing from where I was in the stands. If I remember correctly Groce left the game and didn't come back after that. The rest of Calmus's career whenever I watched an Oklahoma game I prayed someone would knock that fucker out with a career ending injury. I was 15 and full of rage.