Why Keenan Allen is playing with a chip on his shoulder

LOS ANGELES -- In a sport dominated by some of the world's fastest and strongest humans, Los Angeles Chargers wide receiver Keenan Allen is neither.

That was evident during the 2013 NFL draft process for Allen, a 6-foot-2, 211-pounder whom many analysts considered the top receiver. But Allen had suffered a season-ending PCL injury in his final season at the University of California. He ran a 4.71-second 40-yard dash at his pro day -- well behind Marquise Goodwin's 4.27 time that led receivers at the combine.

Chargers wide receivers coach Sanjay Lal, then in the same role with the New York Jets , said he remembers the concerns around Allen.

He was one of the most productive receivers in college -- Allen still holds the school record for receptions (205) and is third in yards (2