NFL's brutality makes it too difficult to accuse players of faking injuries to stop fast offenses like Eagles

Real pain was in the stub of a finger that Arizona Cardinals safety Rashad Johnson pulled from a glove during Sunday's game at New Orleans. Doctors decided they couldn't sew Johnson's tip back on his finger, so they spent the rest of the game trying to cover the exposed bone with skin in hopes of preventing an infection. Needless to say, he did not return since a severed finger is not the kind of injury that gets you back in a ballgame.

And yet none of the 73,057 in the Superdome that day would have watched Johnson walking off the field and thought he was hurt.

So how can a fan look at a player lying on the field, face contorted in agony, as trainers rub a cramp from his leg and say he is faking? How can fans boo someone limping off the field or collapsing in the grass because they believe the ache searing through the man's leg is not real?

On Thursday night in Philadelphia, fans at Lincoln Financial Field booed several defensive players for the Kansas City Chiefs who had leg injuries that required care. They believed these injuries were pretend ailments designed to slow the fast pace of the Eagles' new offense under coach Chip Kelly.

[Watch: Top 5 must-see NFL plays from Sunday]

This is why they booed Chiefs cornerback Brandon Flowers, who came into the game with a knee injury first sustained the week before. They booed as Flowers sat on the ground with trainers all around him. They booed more when the scoreboard showed him standing still and then collapsing to the grass. They booed as he was helped off the field. And they booed even after he left the game.

Maybe those fans who booed should know Flowers did not practice for the Chiefs on Monday and is listed as day-to-day with inflammation in his knee.

"Never, ever going to get into that," Kelly told reporters this past week when asked if he thinks players are faking injuries to slow his offense. "We need to execute better and not turn the ball over. That's the least of my worries right now."

No one can ever judge another man's pain, especially in a sport like football where 250-pound men crash into each other at sprinter speeds. Kelly understands. Any coach understands. Yes, it is frustrating to watch an offense based on pace and timing stall as players fall to the field. Perhaps some of those players are faking those injuries, but more often they aren't.

[Related: Is Johnny Manziel a perfect fit in Chip Kelly's offense? ]

The one player the fans in Philadelphia booed more than Flowers was fellow cornerback Sean Smith, who fell more than once with cramps in his legs. After Smith hobbled off the field, the man doing play-by-play in the stadium press box stumbled over the official announcement of Smith's injury, saying the player was "cramping." This drew laughter in the box from the writers who howled at the muddled syntax. But later Smith showed reporters a bandage on his arm and said it was covering the hole where trainers had placed an IV tube because he was dehydrated.

NFL players lose fluids fast in the early part of the season, when the weather is still hot. Because most starters play only a quarter or two in preseason games, their bodies are not always acclimated for the pace of a full game when the regular season starts. It often takes a month to adjust.

When a team like Philadelphia introduces a racing offense with lots of plays in a short period of time, opponents are going to struggle to catch up, they tire, pass rushers don't get to the quarterback and defensive backs slow down. But an unintended side effect is those same defensive players dehydrate and they get cramps or pull muscles and they fall to the ground, stopping the game and mitigating any advantage of a fast-paced offense.

[Watch: NFC powers stumble to surprising 1-2 starts]

This happened in the Eagles' first game against Washington. As Philadelphia pushed and pushed and pushed down the field, the Redskins wore down and fell to the turf. Suddenly the speedy offense slowed, the Washington players who were left standing caught their breaths and a big Eagles lead fell apart.

In the fourth quarter against Kansas City, Philadelphia found momentum in its offense that it didn't have earlier in the game. The Chiefs were tiring, but they tired too much. An advantage created by the Eagles offense turned into a disadvantage. The game kept stopping, and so did the flow of Kelly's offense.

Not that the fans in Lincoln Financial Field wanted to believe the stoppages were real. Not that the Eagles players, who complained later that the pace of their offense had been disrupted, were willing to accept every Chiefs player's cramp was exactly that.

But the mistake in football is to judge another man's pain in a sport built on violence and deem it to be untrue.