Last Sunday, Mathias Kiwanuka had his arms around Vince Young for a fourth-down sack that would have clinched a win for the New York Giants in Tennessee. Then he inexplicably pulled his arms away, Young took off for 19 yards and the Titans went on to a 24-21 victory.

Kiwanuka's explanation?

He thought Young had thrown the ball and he was afraid that if he brought him down, he'd be flagged for roughing the passer.

It was a strange play that got the rookie defensive end a public chewing out from coach Tom Coughlin when he reached the sideline.

But he got sympathy from Bill Parcells, whose Cowboys took over first place in the NFC East when New York lost.

"Let me tell you what's happened to these defensive players," Parcells said this week. "What's happened to them is they've become so cognizant of not roughing the passer. You can hardly hit them anywhere without getting a penalty. You can't hit them below the waist. You can't hit them with the crown of your helmet. You can't hit them head to head. You can't hit them anywhere."

That's a prevalent opinion around the NFL, especially with defensive players and defense-minded coaches who believe the pendulum has gone too far in the league's desire to protect its most visible and important players. And it can affect games and playoff races, as the play in Tennessee did last Sunday.

Not only was the Kiwanuka play high-profile last weekend, so was one Monday night, when Green Bay's Cullen Jenkins was called for roughing Matt Hasselbeck on a play that otherwise would have ended a Seattle drive with just under 10 minutes left in the game. Instead of being forced to punt, the Seahawks went on to score a clinching touchdown.

What referee Tony Corrente thought from ground level at full speed was a blow to Hasselbeck's head was a blow to his shoulder as the QB turned, something shown clearly on slow-motion replay to viewers around the country. Corrente acknowledged as much this week in a talk with Mike Pereira, the league's supervisor of officials.

"We're going to make mistakes," Pereira said in a telephone conversation with The Associated Press this week.

"Our primary concern is to protect the quarterback. He's the most vulnerable player out there and the rules are designed to keep him healthy. A judgment call in real time from ground level can be different from a slow-motion replay from a better angle."

Indeed. It's often unfair for viewers and television analysts to carry on about bad calls when an on-field official must make an instant decision on a play at full speed. Beyond that, the officials are good enough that most replays demonstrate they were right.

And yet there are those judgment calls, especially roughing the passer, which can be arbitrary, especially with a rule tightened so much recently that some players seem afraid to go near a QB who has released the ball. Or, as in Kiwanuka's case, one who hasn't thrown it yet.

Last month, the Jets' Victor Hobson (on Tom Brady) and the Giants' William Joseph (on David Garrard) were penalized for roughing the passer for taking the quarterbacks to the ground as they released the ball.

How does an athlete weighing more than 250 pounds (Hobson) or 300 (Joseph) stop and let go when they are heading full speed for a player and have him in their grasp when he is about to throw? Those two were penalized because the rule specifies that a defender can't hit a QB in the head or drive him into the turf.

"You cannot drive your whole body weight on top of the player, "Pereira says. "You must take your full weight off the player before he gets to the ground. Drive him to the side."

A tough distinction, especially for 300-pounders with a split-second to turn their body.

"In a game, I think you just have to take your shots when you can get them," says Tennessee defensive end Kyle Vanden Bosch. "It's such a tough debate because I also understand the importance of protecting the quarterback in this league.

"Quarterbacks, especially if a team's starting quarterback goes down, it can really be the end of a season for a team. I understand the importance of protecting quarterbacks, and it's just a tough position. You've got to look at it from both sides."

Sentiments like that from pass rushers make it unlikely the rule will be changed.

Pereira agrees with the rule. Changing it isn't up to him, but his sentiments have a profound influence on the competition committee, which must recommend any change.

In fact, there are some stats this season that indicate defenders are getting more leeway: pass interference calls are down from 159 after 11 weeks last year to 122 this season.

And despite the high-profile roughing-the-passer calls, they actually are slightly down this season, from 80 after 12 weeks in 2005 to 72 this season. That's six a week, not an overwhelming number. "We're not looking for quantity," Pereira says. "We're looking for safety."