The Colts defense has been maligned for a long time. They haven’t had a decent defense since the year the won the Super Bowl back in 2006. And even in that season they still couldn’t stop the run until the playoffs started. It isn’t from lack of trying though.
Indy hired Chuck Pagano back in 2012 to try and fix the defense. He was a defensive mind who was supposed to fix the issues. His 3-4 scheme did not fix anything, and might have made the defense worse. In addition to still not being able to stop the run, the defense didn’t force as many turnovers either.