If you watched the first episode of Netflix’s new documentary series, Full Swing, you know Jordan Spieth and Justin Thomas like to gamble. In the episode, the two PGA Tour stars and longtime friends bet each other $1,000 if they can guess a card out of a deck and $100 if they can throw a golf ball in the hole.

The gambling continues to the golf course, too. During a practice round ahead of the 2022 PGA Championship, Spieth and Thomas play a high-stakes version of the “Hammer Game.” So, what is this betting game Spieth and Thomas play on the golf course, and why shouldn’t you give it a try with your buddies?

The high-stakes gambling game Jordan Spieth and Justin Thomas play during practice rounds

Jordan Spieth and Justin Thomas have combined to earn more than $100 million on the PGA Tour, and that doesn’t even include their off-the-course ventures. Being the competitors they are, the star golfers like to gamble that money on and off the golf course.

Spieth and Thomas play a ton of practice rounds together before PGA Tour events, and we got a glimpse into the high-stakes betting games they play during those non-competitive rounds.

In the first episode of Netflix’s Full Swing, Spieth and Thomas head to Southern Hills in Tulsa, Okla. early to play a practice round ahead of the 2022 PGA Championship. JT suggests on the first tee that they play a version of the “Hammer Game.” Spieth then proposes a “$50 hammer, birdie double,” which is a level of the game most amateurs would shy away from.

Here’s how it works.

In a 1v1 match, the golfers go head-to-head in match play (the lower score on each hole wins the hole). But here’s the catch: One player can “hammer” the other if he thinks he has the advantage, which doubles the bet for that hole. So, if Thomas starts with the hammer and Spieth hits his tee shot in the trees, JT would probably call “hammer” and double the bet from $50 to $100 for that hole. The hammer then switches to the other player, so Spieth would have the opportunity to use it on the same hole if he recovers or save it for another hole. There’s no limit on the number of hammers played on a hole, so it’s possible the bet doubles two or three times on just one hole.

Spieth and JT decided to kick it up a notch by playing “birdie double,” which just means the bet doubles again if either player makes a birdie. For example, if Thomas birdied a hole, Spieth parred, and there were two hammers called on the same hole, the bet doubled three times to go from $50, to $100, to $200, then to $400. JT wins that $400, and they move on to the next hole.

Either player could realistically walk off the 18th green down more than $1,000 in the match. But again, Spieth and Thomas are both multi-millionaires who travel to tournaments together in a private jet. They can handle a tough day on the course, but I wouldn’t recommend their version of the “Hammer Game” to the casual golfers out there.