http://www.freep.com/story/sports/nfl/lions/2016/06/25/detroit-lions-calvin-johnson-camp/86376744/
Calvin Johnson talks retirement, says he was fed up, beat up from football.
Freep

http://www.freep.com/story/sports/n...t-lions-calvin-johnson-social-media/86378280/
Calvin Johnson details retirement plans, explains social media surge.
Freep

http://www.mlive.com/lions/index.ssf/2016/06/calvin_johnson_shuts_door_rega.html#incart_river_index
Former Detroit Lions WR Calvin Johnson makes it clear he intends to stay retired

http://espn.go.com/nfl/story/_/id/1...ceiver-calvin-johnson-says-content-retirement
Former Lions WR Calvin Johnson: 'Things are going good right now'.
espn

His body wasn't holding up anymore and Calvin Johnson had had enough. That, the former Detroit Lions All-Pro receiver said, was a big reason for his retirement.
It had nothing to do with the Lions' record when he was with the team. It had nothing to do with the lack of playoff appearances or Super Bowls. It was just that his body was starting to fail him after knee, ankle and finger surgeries.
Even months after he retired, Johnson wore a splint on his injured finger during his Calvin Johnson Jr. Foundation Catching Dreams Football Camp at L'Anse Creuse High School in Michigan.

http://profootballtalk.nbcsports.com/2016/06/25/megatron-im-content-with-what-i-did-not-coming-back/
Megatron: I’m content with what I did, not coming back.
PFT