Among the Lions’ five returning linebackers, only Tahir Whitehead did not play one snap on defense in 2012. “I had trouble with my alignments and stuff last year,” said Whitehead, a fifth-round pick from Temple in 2012. “So it made me think a lot, instead of being able to play fluid and just flow and just go out there and just play football. This year, I just plan on learning the defense a lot more than I did last year.” Whitehead also wants to put on a few pounds. Last year, he played at 233 pounds. This year, he wants to be closer to 240. “Just knowing that the expectations of me from my first to my second year will be high,” Whitehead said, “I’ve just been working since the end of the season.” It hasn’t gone unnoticed. “You guys might not see the development of a Jason Fox or Tahir Whitehead or Travis Lewis, except for what they do on Sundays in special teams and things like that,” coach Jim Schwartz told reporters recently. “But the accumulation of reps and what they do on the practice field gives us confidence that we’ll be able to find that.”