The Iowa State defense was bad last year. Awful. They were blown out, beat up, and most frustratingly, taken advantage of in key games where one stop would have made a difference. The inability to stop big plays in key moments spelled doom in many of the 9 games they lost. I have discussed the statistical background for that in a previous article (Iowa State Football: The Impact of Explosive Plays).
Offense and defense are different. Yes, an idiotic statement, but the analysis is different.
On offense, you dictate the play and alignment and execute a designated assignment.