Name the change in football conditions that NFL Hall of Famer Dick Butkus blamed for shortening his football career.

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I'm guessing the proliferation of artificial turf stadia !

You are correct reedman!!! artificial turf. While it was first used in the Houston Astrodome, the artificial turf spread to many another stadiums. Butkus claims that the harsh, first generation turf used at Soldier's Field in Chicago aggravated problems with his knees and forced him to cut his career short. Butkus's complaints aren't uncommon, and several teams have moved back from artificial turf to natural grass.