With more than 300 players who weigh more than 300 pounds, the NFL doesn't need a salary cap. It needs a weight cap. (And some slimming pinstripes wouldn't hurt, either.)
How would a weight cap work? You couldn't just place a maximum on the entire roster's weight, because teams would simply circumvent that rule by signing five or so vegan marathoners. Instead, the league should declare that a team can never have more than 2,800 pounds on the field at one time.
The rule wouldn't be difficult to enforce -- just bring in those big truck scales the highway departments use, and place one on each sideline. And it wouldn't take any additional time, either. During a possession change, timeout or commercial break, officials could have the respective offense and defense go over to the sideline and jump on the scales. If it's over the 2,800-pound limit, the team gets nailed for a 10-yard penalty and has to substitute lighter players.
Sure, a weight-cap sounds goofy. But it really isn't when you think about it. The players would be smaller, which means they'd be quicker. Offenses and defenses would be more efficient, because leaner, quicker lines can move the ball and defend better than their sluggish counterparts. The Broncos, after all, currently have the lightest offense in the AFC, but are fourth in the conference in yards per game. The Bills, meanwhile, have the heaviest offense in the AFC, and are next-to-last in yards per game. More importantly, players would be healthier and sustain fewer injuries.
And there would be all sorts of entertaining new strategies. Teams would sign skinny guys just to get under the cap. Or maybe they could bring in their special South Beach Diet packages for short-yardage situations: seven 300-plus-pound linemen and four sub-150-pound defensive backs.