Sport: Upstarts and Upsets in the N.F.L.

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But the biggest rule changes took place on the field. All were aimed at juicing up the offensive game. For the first time, offensive linemen are allowed to extend and lock their arms to fend off the defensive behemoths charging toward spindly quarterbacks.

More important, however, is the new "no-chuck" rule that prohibits defenders from bumping pass receivers once they sprint five yards beyond the line of scrimmage. Most receivers love the new rule, while defending cornerbacks and safeties curse the loss of their principal weapon. Where once defenders brushed, bumped and belted would-be pass catchers with each step, they are now reduced to a single bash as the ball is snapped. Says the Cowboys' top receiver, Drew Pearson: "It's great. Cutting across the field, I used to wind up looking out the earhole of my helmet. Now all I have to worry about is getting hit after I make the catch."

On the other side of the no-chuck fence, Dallas' All-Pro free safety Cliff Harris does not find the Astroturf as green as does Teammate Pearson. Harris complains: "We've had a tough time adjusting to the no-bump rule. We would play close to the line to stop the running game, then we would bump the receivers off their routes and keep on hitting them until the pass was thrown." Adds the Packers' Steve Luke: "It's like a carpenter. He needs both hands to do a good job. If he loses three fingers, his work wouldn't be as good. That rule takes three fingers away from us."

To enforce the new rules, the N.F.L. added a seventh official, and he has been kept busy. Halfway through the season, illegal-chuck penalties were the sixth most frequently called infraction, ranking behind such old favorites as offsides and clipping.

Free now to run their patterns without the constant tattoo of bumps, receivers got still another break from the rulemakers. Before this season, a forward pass tipped by an offensive player had to touch a defender before a second offensive player could catch it legally; it was just such a play, still hotly debated, that won Pittsburgh its first play-off victory over Oakland in 1972. That rule has now been changed to permit open season on all loose balls. Wily Minnesota quarterback Fran Tarkenton lost no time testing the new regulation. In the closing seconds of the first half during an early-season game against Denver, Tarkenton dispatched three receivers to an area no bigger than a washtub, then lobbed the ball into their midst. In a scene reminiscent of N.B.A. teams battling for a rebound, the gambit failed.