It's almost old news at this point, but Calvin Johnson has now made it official, announcing his retirement via a statement on the Detroit Lions' website. He did not offer an explanation, only thanking the Lions and their fans for their support.
Johnson led the league in receiving touchdowns in 2008, in receiving yardage in 2011, and in receptions and yardage (the latter an all-time record of 1,964) in 2012. He finished in the top ten in receptions just twice, but in the top ten for yardage six time and for touchdowns four times. Since he was drafted in 2007, he ranks seventh with 731 catches, but first in yardage (11,619) touchdowns (83), and 100-yard games (46).
He always got a ton of targets in Detroit's high-volume passing game, and so his advanced stats aren't quite as dominant -- he was seventh in DVOA in 2011, his only season in the top ten in that category. But he led the league in DYAR twice and finished in the top ten six times, leading the league in both 2011 and 2012, and finishing eighth last season.