LAS VEGAS -- This is not your typical Friday night on the corner of Tropicana Avenue and Las Vegas Boulevard.

The Professional Bull Riders World Championships are in town, drawing record crowds. Instead of the classic tones of Frank Sinatra and Tony Bennett, country music blares in front of the New York-New York hotel and casino on The Strip. Vests and button-down, long-sleeve shirts, tucked into tight-fitting jeans with showcase belts, are en vogue. Canned beer and cowboy hats are everywhere, as PBR fans mill around outside T-Mobile Arena ahead of the quarterfinal round.

Little do they know that an imposter is on his way: a 44-year-old professional gambler who is in disguise and on a mission to beat the town's bookmakers. But the gig is almost up: The longtime wise-guy hustle he's trying to pull off tonight is on its last leg, and a staple of American sports betting could be on its way out.

Just before 7 p.m., a man pulls up in front of New York-New York in a red Ford with South Dakota plates. It's his buddy's car, he says. We'll call him Cowboy Erik. Tan and stocky with the broad shoulders of a competitive tennis player, he has a short, graying beard and hair to match. He sounds like a vulgar sports-talk radio host from the East Coast. But he isn't.

His outfit for the night looks familiar: vest, button-down, long-sleeve shirt and jeans, with a cowboy hat in the back seat. He's hoping to fool the sportsbooks into thinking he's a naïve, happy-go-lucky tourist in town for a rootin'-tootin' good time.

However, given his untucked shirt and tennis shoes, it's kind of a poor disguise. Ten years ago, he went all-out: big belt buckle, cowboy boots and his best Wyoming accent. It's not worth it anymore.

Indeed, for this pretend cowboy, tonight might be one of his last rides on what for decades has been a moneymaking train: parlay cards.

Long considered a sucker bet -- and they are for most of us -- professional bettors such as Cowboy Erik have been beating parlay cards for decades. But the edge is diminishing, and the hassle is increasing.

"This may be the last year I do this," he says to me before he steps on the gas and we speed off into the Vegas night.

Parlay cards -- the hard-copy, pencil-and-paper betting sheets -- have been commonplace at sportsbooks and, more on the down low, at some local taverns for a century. They gained popularity in early 1900s and were many Americans' first bet, their foray into sports betting.

Traditionally, at sportsbooks in casinos, parlay cards are long and skinny, about the length of a ruler and width of a cocktail napkin. The week's games are listed on the cards with the coinciding odds. To win, you have to make multiple picks and get them all right. If you do, you're treated to payout odds that are normally less than your actual chances of nailing every one of your picks individually.

Never seen a parlay card before? Here's what they look like. ESPN

Here's how noted gambling expert, author and MIT graduate Ed Miller sums up your odds of hitting a three-leg parlay in his latest book "The Logic of Sports Betting":

"Assuming you have no ability to pick good bets, and your bets are all independent of one another, your chance of winning each 50-50 bet is about 50%. That gives the chance that you win all three bets as 0.5 x 0.5 x 0.5 = 0.125 or 12.5%."

Over time, you should hit one out of every eight of your "lock" three-teamers. Unfortunately, the typical payout on a three-teamer is 6-1. That's not great, but it's also not unbeatable for the savvy gambler.

Here's how the pros beat the parlay cards:

• The physical cards are printed early in the week, often on Tuesdays, with the point spreads for the games available at that time. Sportsbooks normally put out the cards on Thursday mornings.

• This is key: The point spreads on the cards don't change, even if an impactful player (such as a quarterback) is ruled out. For example, in Week 10, the Kansas City Chiefs were 3.5-point favorites over the Tennessee Titans on the parlay card, but the current line on the oddsboard had shifted to Chiefs -6. Kansas City quarterback Patrick Mahomes' status for the game had been upgraded late in the week, after the cards were printed, causing the point spread to grow in favor of the Chiefs.

• Professional bettors wait until Friday night or Saturday morning to place their parlay bets. They can bet Tuesday's lines with Friday's information and build their parlay cards around the games with stale point spreads. For example, Chiefs -3.5 would be a play.

• Each point the spread on the parlay card differs from the up-to-date line improves the bettors' odds. Load parlay cards up with enough of these games with stale numbers, and the odds can be flipped in your favor.

Easy enough, right? Not exactly.

Casinos aren't built on letting advantage players such as Cowboy Erik bludgeon their bottom lines. Bookmakers fight back, sometimes eliminating games with stale numbers from being eligible to bet on the cards, requiring supervised approval for any cards over certain amounts or outright refusing to take the wagers altogether. It is perfectly legal for sportsbooks to refuse service to bettors. It doesn't stop bettors from trying, though.

Sneaky bettors target the graveyard shift or wait until the Saturday morning rush to see if they can catch a ticket writer in a hurry. They'll put in parlay cards for varying amounts just to see how much they can bet without having to go through the approval process. They like to hop around from one betting window to the next, testing ticket writers while employing techniques to distract them. Cowboy Erik, for example, has been known to bet a card and give it to the teller as a tip -- anything to get on their good side.

It turns into a bookie-vs.-bettor, cat-and-mouse game that some sportsbooks no longer want to play. Ultimately, it might spell the end of the traditional parlay card, leaving wiseguys with one fewer hustle in their repertoire.

Cowboy Erik in action

Cowboy Erik drives quickly and aggressively. He boasts of knowing the quickest routes from one Las Vegas sportsbook to the next and the best parking spots to get in and out of casinos efficiently.

He's single, and his dog, Wimbledon, normally rides shotgun on his adventures. Tonight, Cowboy Erik is stuck with me.

The first stop is the South Point Casino, an off-the-strip joint with a popular 24-hour sportsbook. Cowboy hat on, Erik strolls past a renowned hot dog cart and moseys over to a side wall next to the betting counter where the parlay cards are. He grabs a dozen cards and heads to the back bar to get to work.

For 15 minutes, he scours the numbers, comparing the point spreads on the cards to the current lines at an influential offshore sportsbook on his phone.

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Southern Cal is a 1.5-point underdog to Arizona State on the card, but with buzz circulating that Sun Devils' quarterback Jayden Daniels might miss the game, the Trojans are growing 1.5-point favorites on the up-to-date board. (Daniels will be ruled out Saturday, and the line will close at USC -4.5).

Cowboy Erik finds similar edges on Boise State, North Texas and Kentucky. He has a list of teams that he and his partners have handicapped: Boston College, Miami (Fla.), East Carolina, Northwestern, Michigan State and South Carolina. He's pleased how many stale numbers there are on the card, and he narrows his list to 11 teams.

He lands on five parlays -- three $80 three-teamers and two $40 10-teamers -- with a mix of his picks on each card. He heads up to the counter, where a young female ticket writer greets him with a smile and begins the transaction.

The amounts are small enough that identification isn't required. Once the bets are processed and accepted, the sportsbooks are prevented from rescinding them. But that doesn't mean the books have to accept them.

Cowboy Erik has his money out and tries to play it cool. The teller looks at the computer screen, pauses and waves a supervisor over. Erik sighs.

After brief discussion, the supervisor accepts each of the three-teamers but only one of the 10-teamers.

"They said they didn't want the other one," Erik says, as he heads away from the counter, stopping to use a couple free drink tickets on bottles of water before hustling out of the casino.

"Always ask for drink tickets," he notes.

The whole process takes 30 minutes, in and out, and then we're off to the next target.

As he speeds out of the South Point parking lot, he swerves around a semi truck blocking an intersection, blindly flirting with oncoming traffic and running a red light. Time, of course, is money for the professional gambler.

Cowboy Erik waits in line at South Point to try to get some parlays in. ESPN

At 7:50 p.m., Cowboy Erik flies into the parking lot at the Gold Coast casino, another off-the-strip local spot and his second stop on a brisk Friday night journey. He circles the parking garage and backs in to a prime spot.

The numbers on the parlay cards at Gold Coast are similar to those at South Point. Within a few minutes, he decides to attempt to put in four $50 four-teamers, featuring USC and North Texas among others at stale lines, and a $75 10-teamer.

The teller calls a supervisor, and Erik's shoulders sink. The book declines to take any of the bets, saying the Southern Miss-North Texas game is no longer available to bet on the cards.

Erik scoffs, "Why even have them out then?" and angrily bolts out of the building.

The supervisor looks over at the ticket writer and says, "I could see cards going away soon."

Erik hops in the car and grumbles, "That's 2019 in a nutshell. It's almost sad."

A double-edged sword for bookmakers

Since 1992, $1.7 billion has been bet on parlay cards with Nevada sportsbooks, according to the UNLV Center for Gaming Research. The books have won a net $553 million on the cards. Comparatively, sportsbooks have won just 4.95% off $31.9 billion bet on football in the same timeframe. So why, with a cushy 30.7% margin on parlay cards, are the books so wary of them?

On any given Sunday, if the wiseguys are extra sneaky and games play out a certain way, the books could get crushed on the cards. It happened to the renowned SuperBook in Las Vegas this September.

"That's the first time that we've taken a large hit [on parlay cards] since, I think, 2012," said Jay Kornegay, a 30-plus-year Las Vegas veteran and the vice president at the SuperBook. "It's been a long time."

In Week 3 of the NFL season, a group of bettors slipped in more than 200 parlay cards featuring advantage sides at The SuperBook. For example, they had the Ravens +6 at Kansas City. The line closed at Chiefs -4.5. Kansas City won but didn't cover 33-28. They mixed in a few college games and capped their cards with under 48 in the Rams-Browns game on Sunday night. Approximately 35 of the "ties win" cards hit -- all 10-teamers at 550-1 odds -- and the SuperBook suffered its worst Sunday loss in years.

Trying to figure out how it happened, Kornegay and his staff reviewed surveillance footage from previous days. They were able to identify a customer who submitted several of the advantage parlay cards before returning a few hours later, in a different shirt, to play more cards.

Cowboy Erik says it wasn't him.

"There are some sharp guys out there who will take advantage of anything they can," Kornegay said, "and certainly there are [a] group of them who will take advantage of those stale numbers on parlay cards. Over the years, we've taken precautions and measures to reduce that from happening."

Bettors and sportsbooks have been playing this game for decades.

Vic Salerno, a Hall of Fame bookmaker now with US Bookmaking, said he had the limits on parlay cards set at $5 when he took a big hit in 2005. He responded by writing software that restricted the number of stale lines that would be accepted on a card.

"We had a weekend when a player played multiple $4 cards to stay under the limit and beat us out of nearly $50,000 playing all the games that had big moves," Salerno recalled.

Cowboy Erik might have been in on the above score, he tells me with a wry smile.

'I thought I was Rain Main'

While speeding down I-15, with the lit-up Vegas skyline on our right, Cowboy Erik tells good stories.

"The first time I came to Vegas, I was playing blackjack at Binion's," the Boston native says. "I felt like I won every hand, and the casino host offered to comp me dinner. I thought I was Rain Man."

He moved to Las Vegas permanently in June 2004, spontaneously quitting his job in real estate and driving cross-country with his old dog, Gekko (after Gordon), in a black 2004 Lexus ES 300. He arrived as an experienced gambler and feasted on novices at the poker tables during his early years in town, but he openly admits that he was a "total square" when it came to sports betting and had lost his fair share on parlay cards to a local bookmaker back home. He was determined to make it as a professional gambler, though, if only to prove his doubters back East wrong.

By April 2005, 10 months after he moved to Las Vegas, he was flat broke and in need of a break. He got one when he stumbled into a professional betting syndicate that took him under its wing and taught him how to win.

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Ahead of the 2005 football season, Cowboy Erik was at a barbecue with his new business partners and asked if there were any money in betting parlay cards.

"They told me we're going to crush these things," Erik recalls. "It was so matter of fact, and I always thought you couldn't beat [them]."

The group had a handful of members. They split up duties and agreed upon set percentages of revenue. In a time before convenient mobile internet, one member would be responsible for staying home to monitor point spreads around the market and relaying the updated lines to the rest of the team, who were on the road bouncing from book to book.

In Week 2 of the 2005 NFL season, Erik's first as part of the syndicate, they hit the parlay card jackpot. All their advantage plays won. Cowboy Erik estimates that the group won around $500,000, if not more, in one week.

"My partner was mad we didn't win more," he says before zipping across a couple lanes and back to catch an interstate exit.

Delaware magic

The cat has been out of the bag about stale number parlays for a long time, and while the strategy happens in Vegas, it certainly hasn't stayed there. In fact, perhaps one of the most efficient and lucrative parlay scores ever played out at a racetrack in Delaware during the 2009 NFL season.

The Delaware Lottery began offering parlay cards on professional football in 2009. To start, parlay cards were offered only at the state's three racetracks. There were some early bumps for the lottery's parlay operation.

A costly error in Delaware Professional gambler Jack Andrews recalled his biggest mistake while playing parlays in Delaware: "Our biggest oops happened the first or second year, right before Christmas. "We identified seven teams that we liked. When we were going through everything, I would read out the numbers that we were going to be circling on the card. For example's sake, let's say Denver is Team No. 3 and Cleveland is No. 4. We wanted to be on Denver. "For whatever reason, when I'm reading out the cards, I said, 'Denver, Team No. 4.' I repeated four all through the cards. So we were actually betting on Cleveland instead of Denver on all our tickets. "That was a week we went 7-0, and because I made that mistake with Cleveland, it cost us, like, $24,000. "That would've been our biggest hit, at the time. "That night, after all the games had been played, I remember standing next to my Christmas tree and calling my partner, saying, 'I screwed up.' "I don't think we ever went 7-0 until the next-to-last season."

"That first year was magical," a professional gambler who goes by the pseudonym Jack Andrews said. "They were dealing these lines that were a good point off, through key numbers."

Andrews and a buddy played at Delaware Park on a weekly basis. They would arrive at the track Sunday morning, grab a handful of cards and then head back out to Andrews' black BMW 330 Coupe to plug the point spreads into a spreadsheet on a laptop and calculate the edges. The driver's seat was too tight for the laptop, so Andrews would crawl into the back seat and do the figures while his partner stayed in the front seat.

Normally by 10:30 a.m. ET, they had landed on their final teams. They'd wait until around 11 a.m. for the injury reports before making final adjustments. At 11:30 a.m., it was time to start filling out the parlay cards by hand, as many as 56 on any given day.

"We'd have Sharpie markers," Andrews said, "because the little pencils they provide take too long. If you have a Sharpie marker, you just kind of blot it down in each circle. That makes the cards go a lot faster."

By noon, they headed to the window. For experienced sportsbook ticket writers, sloppy markings on parlay cards are a common annoyance. Andrews' cards, thanks to the Sharpie, were easy to feed into the machine. It went quickly, and prior to the 1 p.m. kickoffs, with no resistance, Andrews and his partner were allowed to place as many $500 three-team parlays as they wanted. Cowboy Erik would be jealous.

"We had several weeks where we were cashing $20,000 to $30,000," Andrews said.

When the final revenue numbers for the 2009-10 NFL season were released by the lottery, Andrews had accounted for 1% of the $9.5 million bet on parlay cards in Delaware that season.

"It was a beautiful thing for a good eight years or so," Andrews said.

Back in Vegas, it's 8:15 p.m. when Cowboy Erik works his way into an advantage parking spot at The Palms, a high-end casino off The Strip and across the street from Gold Coast. He's pretty exasperated at this point and resigned to the fact that his parlay playing days are coming to an end. The hustle is dying.

Some believe parlay cards altogether might be on their last legs in the rapidly evolving sports betting landscape in the U.S. Some of the European companies that are running sportsbooks in the states with sports betting already don't offer physical parlay cards. MGM sportsbooks in Nevada now offer what are called dynamic parlay cards, featuring barcodes that update the point spreads on the cards automatically when the bet is placed at the counter.

"What's the future of the cards?" Kornegay asks. "There's no doubt that they've been a huge benefit for the books to offer. The physical cards themselves I could see disappearing, but the type of wager, parlays, will always be a part of our operation."

Las Vegas oddsmaker Dave Sharapan says that despite some obstacles, parlay cards are without question good for the books.

"You have to overcome the stale numbers with volume and paying attention," Sharapan said. "I think if you give people a fair shake on the parlay cards, they can be a good thing. At the same time, you can't just set them out anymore and run them when someone comes up. That's for sure."

Can you spot the parlay bettor among fans in Vegas for the Professional Bull Riders World Championships? ESPN

Erik says it was easier to get more parlays in play as recently as five years ago. He and a partner used to go back and forth between sportsbooks at the Gold Coast and The Orleans in downtown Las Vegas and get thousands of dollars down on 40 or so parlay cards in just a few hours. The books were more receptive then.

Sometimes, he'd don a costume, maybe something as simple a pair of sunglasses or a change of shirt. The disguises are more about distracting the teller and reducing suspicion than they are about protecting one's identity.

"Maybe you carry in one of those big yardsticks of beer to distract them," he says.

"If you convince them that you're in town for the rodeo or whatever atmosphere you were trying to blend into, they were more likely to take a chunk of parlay cards. These days, they are so wary of anything that I don't think the disguises really help that much anymore. Once they look at the card and see you've played a few games that the numbers have moved, you could be dressed as Moses, and they're not going to take it."

At the Palms, Cowboy Erik finds advantages on the same group of teams: Chiefs, USC, Boise State and North Texas. He lands on four three-teamers for $40 each and a $50 10-teamer.

"I'm going to try to put the three-teamers in first, and if they take them, pull the 10-teamer out of my pocket and say, 'Oh, I forgot. I got this one, too,'" he says as he heads to the betting counter.

No dice. A supervisor comes over and turns down all but one of his four three-teamers. Erik is not pleased.

"Yeah, that's right. I'm trying to win," he says incredulously to the supervisor and turns away in disgust.

Back in the parking lot, Erik is visibly frustrated. He gets in the car and says, "This is why this is a dying hustle.

"But there's a saying in the advantage player community that when something dies, a new thing usually comes along."