The Los Angeles Express had just finished a late-afternoon practice, looking to Monday night's game here with the Washington Federals. As the shadows of the goalposts lengthened and day started to give way to darkness, one man stayed behind on the grass.

Anthony Davis is 30, trying to make a mark on the USFL as a running back after four years away from football. He stretched out on a patch of fresh-mown grass and reminisced about the eclipse of what had started out as a brilliant career.

"I was on top of the world," he said. "I came in second place for the Heisman in '74. Three Rose Bowls. The Jets drafted me but they thought I was too small and they weren't going to use me as a running back much. So I signed a $1-million-plus guaranteed contract with the Southern California Suns (of the World Football League). And it turned out great."

After the 12th game of the 1975 season, the 5-foot-9 Davis had rushed for 1,200 yards and 16 touchdowns.

"Then it happened," said Davis. "We were in the locker room in Hawaii after beating the Hawaiians. It was the usual thing. There were always some guys complaining about the conditions, about athelete's foot and all that. One guy was wearing a pair of underwear on his head. Everyone was acting a little crazy.

"Well, in the middle of that, our coach, Tom Fears, just walks in and says, 'Gentlemen, the WFL has folded.' I was broken."

Davis' luck did not improve as he took a three-year, errant tour of the football universe.

Davis played with the Toronto Argonauts of the Canadian Football League in 1976. In a preseason game, he broke three bones in his back and was out for the year.

With the Tampa Bay Buccaneers and his old college coach John McKay in 1977, he broke his shoulder in the sixth game.

With the Houston Oilers in 1978, in the backfield with Earl Campbell, Davis caught a pass on the first play of the first preseason game and ended up with a broken leg. When he returned to action more than a month later, he broke the same leg on a kickoff.

"Same leg, same place," says Davis. "I should have stayed home. I was beginning to get the message."

If there was a message being issued, Davis did not take it to heart until the Buccaneers traded him to the Los Angeles Rams in 1978. Following the death of team owner Carroll Rosenbloom, the Rams were a troubled franchise, and after Davis broke a few ribs in an exhibition with the New England Patriots, he decided to make his release from the team an occasion for retirement.

"With the good luck I was having, I knew it was time for something else," Davis says. At USC's vaunted tailback position, Davis became the school's third leading rusher with 3,724 yards. He also earned a degree in speech and drama.

"I was in this one episode of 'Buck Rogers' where I played an Olympic sprinter of the future," he says. "I was all dressed in a kind of silver Saran Wrap and I wore this aero-thing on my head. They called me Antonious Devez."

In "Two-Minute Warning," Davis played Eugene Brooker, a SWAT team commander in a cast led by Charlton Heston. With Bill Murray, he appeared in "Loose Shoes." He was a guard for Angie Dickinson in an episode of "Police Woman" and a transvestite in a Home Box Office extravaganza called "Up To Now."

"I guess my biggest role was in 'Roots,'" says Davis. "Just before I went to the Oilers, I played a friend of Alex Haley's grandfather. The scene was 1896 in Henning, Tenn. I got lynched."

With the arrival of the USFL, Davis thought about recultivating his more advanced talents. Tom Fears, his old WFL coach and now the Los Angeles Express director of player personnel, invited Davis to training camp.

Davis and the Federals' Drew Taylor are playing in their fourth pro league--WFL, CFL, NFL and USFL.

Davis says he has tried to keep in shape by playing racquetball, but he arrived in camp "about 30 pounds over playing weight. I just had to stop eating and I lost the pounds," says Davis.

Last week against the New Jersey Generals, Davis played behind Montana State's Tony Boddie. He carried only three times, and against the Federals Monday night he is not likely to play much more.

"It's all right,"says Davis. "At this point in my life, I'll play when they need me. I'm not 21 anymore. I did have a satisfying moment there last week. I saw Herschel Walker at halftime. He's in a new league with all that pressure on him. I just told him that others have been in his position. I was once where he is now, you know."

Ironically, Boddie broke his left thumb in practice and wore a cast--but said he would be "100 percent," without the cast, Monday night . . . The Federals meanwhile signed their second ex-CFL receiver in a week: Mike Holmes. At 32, the 6-2, 195-pound Holmes rejoins Coach Ray Jauch, for whom he played the past five years in Winnipeg, leading all Blue Bomber receivers in 1979 and 1980.