Christian Hackenberg had his best season as a freshman with the Nittany Lions. He completed 58.9 percent of his passes for 2,955 yards and 20 touchdowns, promising numbers for a young quarterback. Bill O’Brien left to become head coach of the Texans, and Hackenberg didn’t produce the same numbers in his last two seasons in State College.

Without O’Brien, his completion percentage dropped from 55.8 in 2014 to 53.5 in 2015. His yards per attempt dropped. During those two years, Hackenberg threw 28 touchdown passes and 21 interceptions.

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http://espn.go.com/nfl/story/_/id/14849783/christian-hackenberg-houston-texans-bill-obrien-quarterback-future-nfl