Calvin Johnson spoke candidly about his decision to retire after the 2015 season, admitting the Detroit Lions' inability to compete for a Super Bowl played a role in his decision. 

Johnson was asked if he ever considered changing teams.

"Of course, I thought about it," he said. "Just like in basketball, you know, guys, they create these superteams. But it's not quite like that in football where I had the freedom just to go.

"I was stuck in my contract with Detroit, and they told me, they would not release my contract, so I would have to come back to them. I didn't see the chance for them to win a Super Bowl at the time, and for the work I was putting in, it wasn't worth my time to keep on beating my head against the wall and not going anywhere.

"It's the definition of insanity," Johnson added.

Asked again if playing for the Lions was the reason he retired, Johnson said: "Yes, and the body."