Herschel is rolling now: Elway to Broncos; Celtics collapse in playoffs

For a while it appeared millionaire running back Herschel Walker was going to be a bust in the United States Football League. The tide has turned, however, and the powerful rookie of the New Jersey Generals is now earning his stars.

But some people were quick to criticize him after his slow start. One veteran pro football writer even went so far as to say, ''Walker's reputation and reality are leap years apart, and it will be some time - a long time, if ever - when he will be a great runner.''

That was a premature assessment, though. For after averaging only 65 yards in his first four games (well below the 159 he averaged at the University of Georgia), Walker ticked off outings of 177, 133, 143, 138, and 172 yards. That puts him in front of Philadelphia's Kelvin Bryant for the league rushing title, with half the season, or nine games, still to go.

It took a while for the Generals' young line to jell in front of Walker, and a while for Herschel to run out of the pro set. In college he lined up deep in the ''I'' formation, but now he's in a split-back formation that doesn't allow him the same opportunity to see the holes open.

Despite Walker's progress, his team has lagged behind. The Generals, the USFL's ''flagship franchise'' as a result of being in the New York metropolitan area, are a disappointing 3-6. That's a far cry from what Herschel was used to in college, where Georgia lost only one of 28 games in which he ran for 100 yards. Elway to Denver

Can anyone make heads or tails of the John Elway situation?

Herein a quickie replay: The coveted Stanford quarterback is drafted by the Baltimore Colts, a team he doesn't want to play for. He threatens to play baseball (not his best sport) if the Colts don't trade his rights. Then with everybody expecting the Colts to deal him to some West Coast club, lest he sign with the Yankees, John winds up with the Denver Broncos in a shocking transaction. Though not exactly what Elway had in mind, the deal at least gets the league's top draft choice closer to his beloved California.

The deal was made by Colts owner Robert Irsay, who reportedly never consulted with the club's general manager or coach. And he didn't extract a king's ransom in draft choices, Baltimore's original asking price for Elway. What Baltimore got, instead, was Denver's first-round draft choice this year, Northwestern lineman Chris Hinton, reserve quarterback Mark Herrmann, and Denver's No. 1 pick in 1984.

Herrmann initially reacted to the trade by hinting he might retire rather than report to the NFL's worst team. And Hinton, his agent has said, might consider playing for the USFL's Chicago Blitz. Meanwhile, Al Davis, owner of the Los Angeles Raiders, said he may file a suit against the league for ''orchestrating'' the trade for Elway, whom Davis hoped to acquire. Fall of the Celtics

There's no joy in Boston these days, because the once-mighty Celtics have struck out, making an undignified exit from the pro basketball playoffs. They were swept in their best-of-seven quarterfinal series with the Milwaukee Bucks, thus becoming the first Celtic squad to fold in four straight games.

All this might be a little easier to swallow if Boston hadn't won the National Basketball Association championship two years ago. But the Celtics did win in '81, and returned basically the same team this season. If anything, it was better on paper, with the addition of veterans Quinn Buckner and Scott Wedman, plus more experience throughout.

But somehow everything fell apart. The demise has been pinned to a number of factors, including friction between Coach Bill Fitch and his players and an unsettled backcourt rotation that led to confusion. Selfishness, some observers feel, began to infiltrate the ranks. And the Celtic mystique certainly was eroded by the team's inability to play hard against the league's weaker teams. The players found they couldn't just ''turn it on'' in the playoffs.

Facing Milwaukee proved to an especially difficult task, since the Bucks utilized a first-round bye to prepare. For almost two weeks they studied film of every Boston play and defense under the watchful of eye of their coach, Don Nelson, a former Celtic. Boston, meanwhile, was kept occupied in an emotional mini-series with Atlanta. Touching other bases

* What possessed the New York Jets to select quarterback Ken O'Brien of California-Davis on the first round of this year's National Football League draft?

Though he's a virtual unknown Division II player, the Jets feel O'Brien has the arm, leadership, and intelligence to become an outstanding NFL quarterback, given time to develop. And with the job presently in good hands, New York can afford to bring him along slowly behind starter Richard Todd and backup Pat Ryan.

The Jets, of course, could have played it safe and gone after a heralded major college quarterback, since Pittsburgh's Dan Marino was still available. But the Jets could look around the league and see that major college experience wasn't necessary in the cases of such quarterbacks as Ken Anderson, Terry Bradshaw, Phil Simms, Jim Zorn, and Neil Lomax.

* In tennis, a serve wide of the center line may still be good. This happens on clay occasionally when a compressed ball leaves an elongated bounce mark. If the elliptical depression is so near a line that no court surface can be seen between the ellipse and the line, the ball is good.