Minnesota's Percy Harvin returns the opening kick for a touchdown against the Detroit Lions at Ford Field in Detroit. (AP)

During the 2012 offseason, Giants owner John Mara was quoted on the Giants' website saying that the NFL’s Competition Committee has had conversations about eliminating kickoffs to increase player safety. Those conversations may now hold an allure for wishful Lions fans who saw their team lose to the Vikings on Sunday thanks to woeful coverage on Minnesota’s kick and punt returns.

The offense and defense should also shoulder some blame for their share of inefficiency and errors, but it’s impossible to identify any unit other than special teams as the main culprit for Sunday’s defeat.

Offense: C-

Detroit’s first-half offensive struggles continued, as the Lions managed just six points before the break. The difference between Sunday’s game and previous weeks, however, was that they couldn't replicate the second-half offensive explosion that was present in the team's first three games. The passing game did a good job of involving Calvin Johnson and spreading the ball to multiple receivers, but Detroit’s 319 passing yards didn’t translate to red zone success. TE Brandon Pettigrew caught seven of the nine passes thrown his way, but it’s his drop of a sure touchdown in the third quarter that serves as one of the game’s lasting memories.

It’s clear that opponents are abandoning the blitz against the Lions and daring Detroit to beat them with the running game. If that’s the case, the Lions have work to do to be successful. Poor blocking forced Mikel Leshoure to dance in the backfield more than he did during his stellar debut last week, and the Lions managed just 55 rushing yards. It’s clear that the offense can move the ball. To win, they need to learn how to score.

Previous Game’s Grade: B-

Defense: C

It’s tough to fault a defensive unit that didn’t allow a Vikings' offensive touchdown all game, but Minnesota’s inability to find the end zone was as much a product of its own mistakes as the Lions’ ability to stop them. CB Bill Bentley was outclassed by Vikings WR Jerome Simpson all afternoon. He was guilty of a pair of defensive pass interference calls that were a direct result of poor technique. CB Chris Houston and S Ricardo Silva deserve credit for their performances. Houston continues to be the closest thing the Lions have had to a lock-down corner in years, and Silva’s five tackles were impressive given that he was a practice-squad player 48 hours before starting Sunday’s game.

The D-line managed two sacks against Vikings QB Christian Ponder, but the unit’s pressure still has a lot of room for improvement. The run defense had a hit-or-miss feel to it for the entire game. Linebackers Justin Durant and DeAndre Levy made stops in key situations to keep the Lions in the game, but Detroit also allowed Vikings RB Adrian Peterson to break containment and extend several drives. Peterson’s 102-yard rushing performance represents another example of the Lions’ inability to contain the league’s elite running backs on a weekly basis.

Previous Game’s Grade: D+

Special teams: F

Detroit allowed two kick returns for scores for the second consecutive game. Minnesota managed almost as many yards on returns (182) as it did on offense (227). Percy Harvin’s 105-yard kickoff return to start the game was a result of the coverage team’s inability to fight through blocks. Marcus Sherels’ 77-yard punt return score was made possible by several missed tackles. When a coverage team is beaten in all facets, there’s nothing left to do but call the unit’s effort what it was: Total, abject, unabashed failure.

Previous Game’s Grade: D-

Coaching: C

The loss will surely be frustrating for offensive coordinator Scott Linehan and defensive coordinator Gunther Cunningham, but poor execution from players is more to blame for the defeat than the game plan. Linehan continues to employ a balanced strategy that will beat the two-high safety coverage Detroit faces on a weekly basis if run correctly. Cunningham continues to try new pressure schemes in an attempt to jump-start a pass rush that has stagnated over Detroit’s last two losses.

Special teams coordinator Danny Crossman’s schemes, however, leave a lot to be desired. It’s telling that Minnesota’s coaches and players told reporters after the game that the film they watched on Detroit’s special teams unit gave them a blueprint for success. Lions coach Jim Schwartz told reporters after the game that Crossman’s job wasn’t in jeopardy despite the unit’s dismal effort in the last two games. If Detroit’s kick coverage doesn’t improve after the bye, it’s possible Schwartz's stance could -- and should -- change.

Previous Game’s Grade: F

Follow Lions reporter John Kreger on Twitter at @CBSLions and @JohnKreger.