THEIR PROBLEM is simple: They are having too much fun. Johnson smirks or raises an eyebrow in mid speech and Costner cracks up. Or Johnson won't smirk and Costner cracks up. Or no one smirks and Shelton cracks up.

During a break earlier in the day, Costner admits that the filming of Tin Cup comes at an "incredibly inconvenient" time -one suspects he may still be in recovery from the lengthy and much-publicized problems with Waterworld. But, he adds with a smile, "because of Ron, making this movie has been one of the most pleasurable experiences for me. Ron is very good medicine."

Costner is clearly enjoying himself. So is Johnson, who has also had his share of personal and professional problems in recent years. Now he is playing away from type-he's the bad guy who doesn't get the girl-and loving every minute of it. "I can't remember the last time I had more fun doing a movie," he says just prior to shooting his confrontation with Costner. "This guy Simms is interesting cause there are guys just like him on the four. And Ron is great about letting me play him the way I want to." The additional perk is that Johnson adores the game. "What is that they say about golf?" he asks. " 'Your worst day on the golf course is still better than your best day in the office.' Our office right now is the course. What could be better than that?"

And then there is Shelton, who directed what may be the best jock movie of the last twenty years-Bull Durham-and who clearly loves being around the jock world. Bull Durham was a labor of love because it was drawn from Shelton’s years as a minor league baseball player. Tin Cup is a labor of love too: Shelton loves golf.

In fact this script was born on a golf course. Shelton was friends with John Norville, a young writer who once played on the Stanford golf team and the two came up with a mutually beneficial agreement: Shelton helped Norville’s writing and Norville helped Shelton’s golf. "I would say to John, 'Okay, you tell me how to get this shot over the lip of the bunker and Ill tell you how to get your character out of that scene in Act II."' Shelton recalls. "Naturally we kept talking about a golf script." Together they created McAvoy a ne'er-do-well with prodigious talent and an equally prodigious talent for self destruction. This character is perhaps best described by his caddy and sidekick, Romeo Posar (Checch Marin), who, in response to McAvoy's complaint "You didn't have any faith in me," says, "I'm sorry, it’s a habit I've developed being around you all these years."

McAvoy is the golfer who will always go for the spectacular shot even when the unspectacular is called for. Norville remembers watching Chip Beck, trailing by three shots in the 1993 Masters, lay up short of the water on the Par-5 fifteenth hole, rather than try to reach the green in two. "I called Ron and said, 'Our guy will never do that: he’ll never lay up’.” Norville recalls. "Chip Beck played brilliant golf for 72 holes, but he'll always be remembered for laying up." When they got deeper into their research, Norville and Shelton both came to believe that using Beck is the example of the guy who lays up was unfair. Other pros told them that Beck is one of the tougher competitors on tour. "We had the right idea but the wrong role model." Shelton says. "It was not a 1-in-10 shot-it was a 1-in-250 shot. Going for it would have been stupid."

Of course, McAvoy wouldn't have laid up if the odds were 1 in 5,000. Which is very much a part of the story.

There are moments when Costner's McAvoy is speaking dreamily about the wonders of golf and you can shut your eyes and hear Costner as Bull Durham’s Crash Davis talking about "the Show." or the things he believes in, like good scotch and the small of a woman's back. But, as everyone on the set is quick to point out, McAvoy is not Davis. “I do tend to write speeches, and when you hear them coming out of Kevin’s mouth, I suppose you can think that this guy is a lot like Crash,” Shelton says. “But Crash is much more of a cynic, and a ruthlessly hard worker.” Crash Davis is also more of a finished product, a man of the world who has reached the end of his career. Tin Cup, on the other hand, hasn’t been anywhere or done anything. And-because golf is so different from baseball-Tin Cup could, conceivably, be at the beginning of his career, even though he's about the same age as Crash.

Or, as Johnson puts it, "the movie is basically about a couple of twelve-year-old boys."

The twelve-year-olds in question would be, McAvoy and Simms. When Shelton and Norville were creating the characters, they wanted one golfer who will always gamble and another who will never gamble, Naturally, the non-gambler, Simms, is the successful one, the millionaire awash in endorsements, flashy clothes, and women. McAvoy has all the talent and all the shots, Simms has everything else, including the girl: Dr. Molly Griswold, a brilliant but slightly off-center psychologist played by Rene Russo. As with Johnson, Shelton went against type in casting Russo, who is often better known for playing smart, serious women, like the doctor in Outbreak and the Secret Service agent in In the Line of Fire. Shelton says he had never seriously considered Russo for the part but was persuaded to let her read for it. “About five minutes after she started, I knew she was Molly," he says. "She had a kind of wacky quality that I had never seen in her other roles, I guess because she'd never tapped into that."

The other key role is that of Romeo Posar, McAvoy's caddy, best friend, and confidant. When Cheech Marin read the script, he was convinced that Posar represented a huge opportunity for him to break away from constantly being described as half of Cheech and Chong. "Seventeen years I did Cheech and Chong," he says. "Now I want to be taken seriously as an actor on my own." Shelton estimates he had 60 Latino actors read for the role-Marin insists it was closer to 80-bcfore he selected Marin to be Posar. Throughout filming, he gave all the actors a wide berth to improvise, but no one more than Marin. In one scene, when McAvoy and Posar stumble into a picture-taking ceremony involving defending U.S. Open champion Pavin, Posar turns to Pavin and says, "Hey, Corey Pavin, you're my biggest fan" Marin made the line up on the spot. Hearing it, Costner threw his arms up into the air and said, "Jeez, Cheech, are you going to steal every scene in this movie?"

For Johnson, Russo, and Marin, their characters represent something of a departure: Johnson plays a bad guy; Russo does comedy; Marin mixes some very serious moments with his one-liners. The only two major players in Tin Cup who are on familiar turf are Shelton and Costner. That makes sense. Shelton wrote the script for Costner; Costner is doing the movie because of Shelton. McAvoy may not be Crash Davis, but he is most certainly a Costner-Shelton character. Only Shelton could create him; only Costner could play him.

THE BIGGEST Buzz around the movie while it is being shot concerns Costner's golf. Although Johnson didn't take up the game until he was an adult, he is an avid player who keeps his handicap in very respectable single digits most of the time. He already knew a number of top touring pros, like Pavin and Payne Stewart, having played in many pro-ams with them. It didn't take too much work to adjust his golf swing to make him look like a pro-although he insists that the new swing is hurting his game. "I look better," he says, smiling. "I'm playing worse."

Costner is a different story he played occasionally as a kid and very occasionally as an adult. "Once a year maybe," he says. "You know, go out and play on vacation with your father-in-law. That type of thing. I could never justify four or five hours a day working at the game." Once he had read the script and knew he was going to play McAvoy. Costner made a point of trying to play some golf while he was in Europe promoting Waterworld. But he did not begin in Earnest until he met with Gary McCord last August at the NEC World Series of Golf in Akron, Ohio.

McCord was a journeyman touring pro who found stardom when he went to work as a commentator for CBS ten years ago. His sharp wit and willingness to poke fun at the all-too serious nature of the tour made him popular with most fans, although not so popular with the less-than-hilarious group of men who run the Masters. They had him banned after the 1994 tournament, when he said (among other things) that the greens at the Augusta National Golf Club were so slick they appeared to have been "bikini waxed," Naturally, the ban only made McCord more famous and made him that much more attractive to Shelton who thinks of stuffiness as a disease-when he was looking for a consultant.

McCord took one look at Costner at their first meeting in August and reported back to Shelton: "We're going to have to find a stand in." Costner had, essentially, no clue about how to handle a club, and, with filming only a few weeks away. McCord began stalking the tour's practice ranges in search of someone who could make the swings that Costner was supposed to make. But during the lessons McCord was giving Costner, he begin to notice something remarkable: Costner's swing was becoming noticeably better.

"I think it his to do with being an actor," McCord says. "He's spent his lifetime mimicking things, copying what other people do, recreating himself. He did the same thing with the golf swing. I've never seen anything like it. Of course, if he wasn't a good athlete, it wouldn't have worked no matter how good an actor he was." By the time filming began in Arizona in late September, stories about Costner’s swing and his newfound addiction to golf were making the rounds on the PGA Tour. They were, as one might expect, exaggerated. "It almost sounded like they had created some kind of bionic golfer," Costner says. "First of all, I wasn't a complete beginner. Second of all, yes, I find myself liking golf more now but I still think finding five hours in a day for it when this movie is over is going to be tough for me."

Still, Costner's improvement was extraordinary. During filming, Johnson was constantly amazed at the shots Costner pulled off with cameras rolling. "He'll hit some shots that are so good he doesn't even understand how good they are," Johnson says, "and then just stand there like it's no big deal. A couple of times I've said to him, 'you know, Kevin, pros hit a three-wood 250 yards all the time. But we mortals just don't do that.' “When shooting moved from Arizona to suburban Houston for the U.S. Open scenes (because of the grass type and the availability of a course that had not yet been opened and could therefore be set up to look like an Open site), it sometimes seemed as if everyone on the set were afflicted with golf-mania. Free moments were an excuse to run to the range for a few swings. Off days were spent at a golf course. The pros clearly enjoyed being around the actors; the actors just as clearly enjoyed watching the pros perform their miracles. Marin had his ten-year-old son with him on the set for several days and their free time was spent playing golf.

The exception to all this was Russo, who, by her own admission, has tailored her interest in sports to suit the men she's dated. "I went out with one guy who liked the Rams," she says, "so I got to know all about the Rams. Then I went out with someone who liked baseball, so I got interested in that for a while. Now, my husband likes to play golf." In a sense, Russo is perfect to play Molly because she too is a golf novice trying to understand the appeal of the game to the man in her life. Molly is the character whom non golfers-especially women-will relate to. While McAvoy and Simms are totally immersed in the game and in trying to hustle one another, Molly stands off to the side, attempting to figure out what these two guys are trying to prove.

Of course, that is a universal truth in the jock world: Trying to prove something often isn't nearly is important is actually believing there's something in a game worth proving.

IT IS AFTER 5 O'CLOCK. The putting green scene has finally been finished, and Shelton is absolutely determined to get one more scene done before dark. Everyone hops on to golf carts to head for the far side of the course. Costner pauses just long enough to make certain that his parents, who have just arrived on the set, and his seven-year-old son have a ride. Then the caravan takes off, dodging and darting along cart paths, taking shortcuts through the woods and across fairways. As soon as they arrive at the shooting site, everyone is shouting at once. Fred Couples and Pavin are in place on one fairway; Costner and Johnson on the other. The extras are given final instructions on how to react as the appreciative gallery when the players come by.

”You know, this is really fun,” Couples says to Pavin.

”Yeah,” Pavin says with a grin, “It feels like we’re making a movie or something.

If you were filming a scene about filming a movie, this would be it. Shelton is everywhere, trying to make sure that Costner and Johnson, who are more than 100 yards away from Couples and Pavin, are in sync with them as they move up one fairway in one direction and the pros walk up the adjoining fairway in the opposite direction. The scene is simple: Costner hits a shot, the gallery explodes, and Pavin and Couples look over their shoulders and notice that McAvoy has moved into a tie for the lead. Pavin then says to Couples: “I can’t believe that the name below mine on the U.S. Open trophy might be Tin Cup.” It is a line only Pavin can deliver, because at the time of filming, only he is the reigning U.S Open champion. Darkness is closing in as they shoot the scene, then reshoot it. Finally, Shelton lets put a yell: ”That’s it, guys, we got it!”

Everyone cheers. The extras are thanked vociferously for their help during the day and sent home. The actors and the golfers congratulate one another, and then everyone jumps on the carts to head back to the clubhouse area. Johnson has a souped up cart and he races past the others transforming himself briefly from golfer to Indy rice-cir driver. "Might be my next part," he says. "You never know in this business."

EVERYONE SEEMS to be having a great time on the set. Yet there is clearly a lot at stake. As proud as he was of Bull Durham, as pleased is he was with the box office for White Men Can’t Jump, Shelton was disappointed that so few people saw Cobb, his most recent jock film, because he thought it was, in its own way, every bit as good as Bull Durham. "All I can do is say. "This is what I set out to do and I did it.” He explains. "After that it's out of my control."

Shelton isn't the only one hoping his luck will change. Costner probably won't look back on 1995 fondly. In spite of all the spinning the hypemeisters have done to make Waterworld sound like it was a success. He appears relatively relaxed on the set, especially one afternoon when his parents and son make cameo appearances in the movie while he stands behind the scenes rolling his video camera-the proud parent and son all at once. But relaxed is a relative word for Costner. When he talks about the bittersweet nature of many of his characters- “Usually I either don’t get the girl, or I get killed,” he says-he almost seems to be talking about himself. He’s rich, famous, talented, and successful, but is he happy? When asked about life in the spotlight, he replies, “I’m not exhausted, but I’m ready to go away for awhile when this picture is over.”

Johnson has no problem with the spotlight. Each day on the set, he appears to be having more fun than anybody. As played by Johnson, David Simms is tough, mean, smart, and every bit as competitive as McAvoy. There are moments when he even out hustles the hustler. "I like this guy," Johnson says. "What's interesting about him is, he's all the terrible things that McAvoy says he is, but it doesn't matter. He knows what he is and he's perfectly comfortable being that person."

Exactly how much Tin Cup costs to make is a closely guarded secret, but it is a fair guess, considering the logistical difficulties of giving people a sense of sprawling grounds of a golf course-not to mention all the extras needed as fans and marshals and Shelton’s insistence on re-creating things exactly as they would be at a U.S. Open-that the final numbers won’t be low. That means that the public has to fall in love with this Costner character the way it fell in love with Crash Davis: it has to believe that Russo is worth fighting for and it has to accept a Johnson it isn’t used to. Most important, it has to care about a golfer. Given golf’s reputation as a sport of the elitist rich, can it happen?

Shelton thinks so. “Golf is a blue collar, working class sport,” he says. “It has an image of being elitist that may be what you see on TV, at the big shot country clubs, but all the guys watching golf are muni players who have to get up at 5:30 on Sunday mornings just to get a tee time. McAvoy is a driving range guy and that’s who his friends are. The movie is about them. It’s the kind of movie that the guys who play at public courses will identify with and the kind of character they’ll fall for.”

He hopes.

There’s no question that golf is hot right now. Television ratings are up: more people are playing the game every year: and equipment sales are soaring. And there is no question that Tin Cup is a lot of fun to make for everyone involved. Even though McAvoy is markedly different from Crash Davis, the movie brings Shelton and Costner back to what they do best: creating fantasy out of reality.

There are just enough stories out there about golfers coming out of nowhere-Lee Trevino, for one-to become big stars, that Shelton and Norville’s story has a ring of truth to it that is sustained almost to the end. If, as Shelton says, the goal is to make the fanatic walk away saying, "Yep, he got it right," while the non fanatic says, "Gee, I didn't understand any of that golf stuff, but that sure was fun," then Tin Cup should work.

And why not? After all, any movie that can make golfers laugh at golf can't be all bad.