As you get older, you really have to learn to pick your opponents. Ask Larry Holmes and Billy Martin.

Holmes felt safe Saturday night. So did Martin. Holmes was fighting a light heavyweight instead of somebody his own size. Martin wasn't even trying to punch a doggie, just be a peacemaker.

Today's lesson: beware new roles.

You never know when your number's up. One day, Larry and Billy were the undefeated heavyweight and lightweight champs of the world. The next, they got what they asked for.

Friends have told Holmes and Martin for years that they were too old for prize rings and hotel bars. But noooo.

Holmes just had to handpick enough victims to break Rocky Marciano's record of retiring 49-0. Nobody thought the uninspiring Holmes deserved to chip away at The Rock. Except Holmes.

He got fair warning in win No. 48 when unknown Carl (The Truth) Williams probably licked him, then got decisioned by the judges.

To quit at 48-0 would have been so classy that Holmes' reputation might have grown with the years. From a fellow who had the great luck never to fight a man of quality in his prime, Holmes eventually might have been seen as a sportsman who knew his true place as a good and graceful but not great champion.

Instead, Holmes had the gall to schedule his 49th win for the 30th anniversary of Marciano's final fight. As his victim, the 220-pound Holmes picked the handsomer Spinks brother (Michael), who competes at 175 pounds.

Spinks showed up at 200 and thumped the flabby Holmes like a washtub. Holmes left himself a legacy all right: first heavyweight champion ever to lose to a light heavyweight in a heavyweight title fight.

Afterward, in one bitter minute of defeat, Holmes gave himself a worse bloody nose than any foe ever did.

"You are freeloading off your dead brother," shouted Holmes at Marciano's brother, Peter. ". . . This is my press conference, you can just shut up. You can go back to Boston or wherever you came from and shove it . . . You can never do what I've done."

What he didn't know was that by opening his mouth, he left himself exposed to a thousand body shots.

Holmes apologized, sort of. And yesterday, he told the Associated Press from his office in Easton, Pa.: "I want to offer my apologies to Rocky Marciano's family for remarks I made at the press conference . . . If I hurt Marciano's family, I regret it."

Holmes' weekend in Las Vegas was a party next to Martin's visit to Baltimore.

Martin had had a tough week before he ever got to the Cross Keys Inn bar.

His team had lost eight in a row to trash its pennant chances. His owner had blasted him for mismanaging a crucial game. He'd hung star rookie Brian Fisher out to dry for six ninth-inning runs in one game, then let Ron Guidry stay in to give up five homers in the next.

Martin also ordered lefty Mike Pagliarulo to bat right-handed against a southpaw, leaving the rookie, who had experimented with switch-hitting in the minors, to bat right-handed for the first time in his major league career. He was out.

Then, Martin scratched his nose. Normally, that'd be pretty safe. Except Martin forgot it was his pitchout sign. The result: "The first 2-0 pitchout I ever saw," according to Orioles Manager Earl Weaver. As Orioles yelled, "Do it again, Billy," the batter walked, the eventual game-winning run trotted to second base and the next man singled him home.

This only gets us to Friday night, mind you. Fade to the Cross Keys bar. Martin says the trouble started when, generous soul that he is, he bought champagne for a newlywed couple. The bridegroom disagrees. Says Martin discussed his new wife's "pot belly."

Martin claims it was "another woman" who merited his pot belly cracks. In the end, Martin and his new friend the bridegroom decided to dance awhile. The usual security guards, who materialize wherever Martin goes, restored order. No bloodshed.

Soon, Billy was fast asleep and ready for a new day. He'd be back. "I didn't get to that guy," said Martin. "But I was in the mood."

Hide the good crystal.

Before reviewing Saturday's history-making events, let's be fair. Martin is an unlucky guy. Think of all the times you've been in a motel bar at 2 a.m. and decided somebody nearby was uglier than you. A pot belly. Big ears. Maybe a protuberant proboscis. Or what if a guy says he's a marshmallow salesman. How can you let a chance like that pass?

Normally, on such occasions, 230-pound Yankees coach Willie Horton is at Martin's elbow. Three hours after Martin returned as Yankees manager in April, Horton arrived by express mail. "Nobody is going to mess with me with this big (guy). . . here," announced Martin.

According to Martin, who's usually the best source for explaining why his brawls are somebody else's fault, the Saturday night melee in which the Yankees manager was kicked, punched, bounced off several walls and had his arm broken was just a silly misunderstanding.

It's a coincidence that the fellow who used Martin as a medicine ball was pitcher Ed Whitson -- the same man whom Martin jerked from the rotation Friday, referring to him as "Whatchamacallit."

Martin says he was just trying to keep Whitson out of a barroom fight. Of course, no fight had actually started. And "the other man," like the potbellied woman of the night before, has not been identified or found.

Anyway, Martin says a fight was brewing. Why argue? Who'd know better?

"He turned on me and went crazy," Martin said.

When the room settled, the security guards -- by now on 24-hour red alert -- were counting over Martin.

Martin and Whatchamacallit were reunited outside the Cross Keys. For details, see previous fight.

"I don't see why I have any problem," said Martin on Sunday in cast and sling. "I don't think I did anything. Once I'm a peacemaker and once it was a kook . . . I run into a lot of kooks. They seek me out."

Opposites attract.

"I'm fine other than that now I'm left-handed," Martin reported.

"I'll pitch him," continued Martin, that name slipping his mind again. "And I'll yank him out, too, if he has to be yanked. But I'll watch his feet."

Events now seem to have proved conclusively that Holmes is no longer safe in a ring nor Martin in a bar. They're marked men in their pet places.

Having graciously attributed his defeat to "Spinks' awkwardness," Holmes has chosen the wise path of retirement.

Boxing probably can endure without Holmes, but baseball just wouldn't be baseball without Martin in a hotel bar.