Chargers vs. Vikings: Biggest Keys for Both Sides in Vital Preseason Contest

Week 3 of the 2012 NFL preseason continues tonight and one of the biggest games on tap is in Minnesota, as the Vikings take on the visiting San Diego Chargers.

As always is the case in the National Football League, the third preseason game is most vital to both teams' regular-season chances.

Starters on each side will likely play through the first half and could even stretch into the third quarter, as coaches look to see how the first-stringers work as a cohesive unit.

For both Minnesota and San Diego, this game is important for a myriad of reasons. For a preview of tonight's contest, here's a look at the biggest keys for the Chargers and Vikings.

San Diego Chargers

Stay Healthy

The only way Philip Rivers will be able to make up for his mediocre 2011 campaign is if the players around him stay healthy. 

Starting running back Ryan Mathews and No. 1 receiver Vincent Brown have both already gone down with injuries that will last into the regular season. In addition, tackle Jared Gaither has battled back spasms all preseason, leaving rookie Michael Harris as the only suitable guy on the quarterback's blind side.

These injuries leave the Chargers so noticeably thin on offense that Rivers may suggest putting tight end Antonio Gates and receiver Malcolm Floyd in bubble wrap until the regular season starts.

Keeping everyone healthy is necessary for head coach Norv Turner tonight.

Minnesota Vikings

Get Another Good Performance From Christian Ponder

After an up-and-down (at best) rookie campaign from Ponder, many analysts openly wondered if the former Florida State Seminole could live up to his first-round pedigree.

Ponder struggled to complete passes, throwing at a 54.1 percent rate, while tossing 13 interceptions in just 11 games.

But through two games this preseason, Ponder has looked infinitely more efficient behind center.

Playing against the Buffalo Bills and San Francisco 49ers, two non-slouch defenses to say the least, Ponder has gone 14-of-22 (63.6 percent) for 216 yards and one touchdown. The real key, though? Zero picks.

Tonight will see Ponder receive his most extensive action of the preseason, again against a top-half defense from last season.

If the second-year quarterback can take the reins again Friday, there's a ton of reason for hope in Minnesota.

Figure Out the Linebacking Corps

Just about the only thing we can be sure of right now with the Vikings linebackers is that Chad Greenway will keep his spot.

But with Jasper Brinkley and Erin Henderson, there are more questions than answers.

The Vikings allowed nearly 200 yards rushing in the first half against the San Francisco 49ers, calling into question the defense as a whole. Chief among those concerns are Brinkley and Henderson, two guys who have looked like fringe starters at the very best so far this preseason.

If Minnesota doesn't want weaknesses against both the pass and run, then head coach Leslie Frazier is going to have to figure out how to scheme for his linebackers.