If a substitution is made by the offense, the offense shall not be permitted to snap the ball until the defense has been permitted to respond with its substitutions. While in the process of a substitution . . . the offense is prohibited from rushing quickly to the line of scrimmage and snapping the ball in an obvious attempt to cause a defensive foul (i.e., too many men on the field). If, in the judgment of the officials, this occurs, the following procedure will apply:

(a) The Umpire shall stand over the ball until the Referee deems that the defense has had a reasonable time to complete its substitutions . . .

- Official NFL Playing Rules, Rule 5, Section 2, Article 10

EAGLES COACH Chip Kelly undoubtedly has many goals this season, only some of which he is likely to share with the public. We cannot know if he has a number of wins in his head for the 2013 season. We cannot know a lot of things. But you can be certain that he is attempting to install an up-tempo, forward-thinking culture into a building that had grown stale.

So far, we have heard this could mean shorter workdays for the players with less down time. We also have seen, on the practice field, a premium being put on pace and just a blizzard of activity.

We see all of that happening. Once the games start, though, there will be another goal - unstated but very real for a coach who really seems to want to create the highest-tempo offense the NFL has ever seem.

Simply, that goal is to make sure the umpire stays the hell out of the way.

Which, when you say that to offensive coordinator Pat Shurmur, brings a laugh. But it is a very serious part of this process. If the NFL decides that Kelly's offense is too fast, the league can rein it in by instructing the umpire to slow things down. If all of his teaching and all of those hand signals from the sideline work too well, and enough opponents complain, a lightning-fast offense can be braked into a simply fast offense by the guys in the striped shirts.

"It's going to be interesting to see," Shurmur said. "I think you've got some evidence now of teams trying to play with tempo in the NFL from the last year or so. I'm sure there's been some conversation in the offseason about what might be coming in the NFL to a greater degree.

"[Tempo] affects everything - the offense, the defense, and how they officiate it. I don't know how it's going to play out. We'll have to see."

Much of the evidence to which Shurmur referred came from the Patriots, who played faster than any NFL team last year, and by a good margin, mostly after coach Bill Belichick bought into the concepts brought to him by former offensive coordinator Bill O'Brien, now at Penn State, who learned them from his old college coaching friend, Chip Kelly.

The Pats really shook a couple of teams with their pace. After the Jets watched the Pats run Denver ragged, they decided that they had seen enough, not only calling the league but also going on a full-scale publicity campaign.

Or, as then-defensive coordinator Mike Pettine was quoted as saying, "If the officials permit [the Patriots] to do that, then the game is going to become chaos.''

(To which, Kelly might mumble under his breath, "Exactly.")

Anyway, you have to think that Kelly will try to push the tempo even more than the Patriots did, if that is possible. The way the rules are written, if the offense does not substitute, there is no restriction on how fast they can run the next play as long as the officials have spotted the ball and the offense is set for 1 second at the line of scrimmage. There also are no restrictions in the last 2 minutes of a half, even if you do substitute.

But the rest of the time, the defense must be given a chance to substitute if the offense does. But how much time? The rule does not specify. If the referee feels as if the offense is going too fast after a substitution, he instructs the umpire to stand over the ball and prevent it from being snapped.

But for how long?

"It's a feel," Shurmur said.

The Eagles will begin to find out this summer, when the officials make their annual camp visit, how this might begin to play out. But the enforcement could vary from week to week, and the offense is going to have to be able to operate accordingly. Again, one way to limit the officials' involvement is not to substitute, which puts a premium on versatility - especially for tight ends and receivers.

"I think it's important," Shurmur said. "You'd like to be able to put a really good running back in the backfield with a really good quarterback, then have four other guys that can play - be able to call the counts up and guys line up wherever and run it."

And if the Eagles can do that, the only thing that can slow them down is themselves.

Today on PhillyDailyNews.com: A source tells Les Bowen that Kenny Phillips and his sore knee may be practicing next week.

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