Philadelphia Eagles coach Chip Kelly's up-tempo offense might have a deterrent.

Not players unable to run it. Not opponents able to stop it. But referees slowing it down.

"We have to make sure teams understand that they don't control the tempo; our officials do" NFL vice president of officiating Dean Blandino told The Wall Street Journal on Monday. "We're going through our normal ball mechanics. We aren't going to rush (unless) it's in the two-minute drill."

Those normal game-slowing mechanics include: changing balls when a play goes out of bounds or on an incomplete pass; the referee who spots the ball positioning himself behind the deepest offensive back before the snap; and allowing the defense to substitute after an offensive substitution.

Neither Kelly nor the Eagles commented on the story but Blandino told the newspaper that the first-year NFL coach didn't show any "overconcern" about these changes when the two met in Philadelphia.

The pace question isn't a new concern for teams. In 2010 the Peyton Manning-led Indianapolis Colts took issue with the time it took for the referee to get to his new-at-the-time spot behind the running back. Even last season teams took issue with how fast Tom Brady and the New England Patriots ran their no-huddle offense. New York Jets linebacker Calvin Pace even defined it as "borderline illegal."