What He's Done
Woodhead has spent the previous three seasons as a third down back in New England. Over those three years, Woodhead totaled 250 carries for 1199 yards and 10 touchdowns. He was also a solid threat in the passing game, hauling in 92 passes for 982 yards and 4 touchdowns over that same span. Woodhead was the top running back in receiving DVOA in 2010 and second best in 2012.
Several solid options already on the roster at running back, New England opted to let Woodhead go. Tom Telesco quickly signed Woodhead to a 2-year, $3.5 million contract
Why He's Here
If the past two seasons are any indication, Ryan Mathews will likely find himself missing playing time at one point or another this season. If that happens, it will be on Woodhead to make sure the running game does not falter.
Even if Mathews stays healthy, Woodhead will likely be seeing plenty of time on the field as the third down back. Mathews still has a ways to go in terms of pass protection, where Woodhead has excelled in the past as a third down back. Woodhead will play a large role in determining how well the Chargers convert third downs this season, either by blocking free pass rushers, or catching the ball out of the backfield.
Why He's Not Higher
It is questionable if Woodhead could handle duties greater than those he was given in New England if asked to do so. Much of Woodhead's success came against 6 man fronts, as the defense was worrying more about Tom Brady and the passing game.
If the Chargers are going to succeed this season, they will likely have to do it with Mathews being the feature back and staying healthy. Woodhead has shown he is great in the role the Chargers will use him in, but it remains to be seen if he could continue that success if the occasion arises that he is asked to do more.
If the Chargers can keep him around 125 touches for the season, he should put up a solid campaign for the Chargers, with 850 or so total yards. We don't know how well he will do if asked to handle 200+ touches in a season, but I suspect there was a reason he was never really the main guy in New England.