ATLANTA—Sahith Theegala is 98 or 99 percent sure he moved some sand while taking a swing out of a bunker at East Lake Golf Club.

Unsure of the precise rule in question, Theegala let playing partner Xander Schauffele and PGA Tour rules officials know. He ended up accepting a two-stroke penalty for the infraction on the third hole, which could have derailed his weekend at the Tour Championship and cost him hundreds of thousands of dollars—not hyperbole.

The FedEx Cup payout is $25 million to the champion, $12.5 million for second place and $7.5 million for third.

Theegala sits in third at 17 under–behind Scottie Scheffler (–26) and Collin Morikawa (–21).

But if Theegala wants to forget the miscue at No. 3, he authored a back nine that was far more memorable. The 26-year-old ran off birdies on seven of his final eight holes, including Nos. 14 through 18, vaulting him to third place after three rounds Saturday at the tour’s season finale.

“Just some momentum putts that kind of kept the birdies going,” Theegala said. “Yeah, it just felt like a lot of my game is really feeling good right now.”

His 5–under 66 could have been a 7–under 64 if not for the penalty.

Theegala, a youngster on tour playing in his second Tour Championship, hit his drive at the par-4 third into a bunker. He described having an unusually good lie, with his ball sitting up in the sand, and as he began his backswing, he was reasonably sure he saw some grains of sand fly with the clubhead.

The well-known edict in the rules of golf is that players cannot ground their club in the sand when addressing their ball. Theegala didn’t know if that also applied to the backswing. Rules officials informed him it would be a two-stroke penalty, turning his par at No. 3 into a double bogey.

“Unfortunately the rule is it doesn’t matter the intent,” Theegala explained after his round. “If you change the lie in the direct area around the ball that could affect your swing, it is a two-shot penalty.

“It was just unfortunate. But I did—pretty sure I breached the rules, so I’m paying the price for it, and I feel good about it.”

Theegala had the opportunity to review the video with rules officials before signing his card. There was no conclusive video evidence to overturn the penalty.

Theegala said he would have slept better if he had seen his suspicion confirmed on camera. But if he hadn’t called the penalty on himself?

“Oh, I wouldn’t be able to sleep,” he said. “No matter what the outcome was, I needed to know what the actual rule was.

“I decided to call the rules official right away on that green. But either way, I would have asked the rules officials after the round, too, or somehow found out what the rule was, and if I didn’t ask a rules official and I went back home and looked up the rule—it was sitting in my mind.”

It was tough for Theegala to move on right away. He said he chucked his water bottle after playing the hole.

“I wear my emotions on my sleeve. Tough to not get upset about that,” Theegala said. “I made a huge par on 4. Thought that saved my round.

“Yeah, I’m just really happy I made that putt because if I didn’t make that putt, I would have been really hot walking to hole 5. Yeah, just gave a little bit more fuel to the fire, I guess. Just tried to use that positively. My caddie, Carl (Smith), kept telling me that I’ve been playing awesome. ‘Just keep doing your thing. Two shots is a lot, but at the end of the day you’ve got a lot more golf to play.'”

It took until the par-3 11th hole for that fire to turn into some positive scores; Theegala landed his tee shot 6 feet away from the pin and made birdie. A 10-footer at the par-5 14th kicked off his closing surge, which included an approach to inside 3 feet on No. 17 and a great pitch on No. 18 that left him a tap-in.

Theegala could have been disqualified from the event if the penalty went ignored and it was discovered later. Still, the decision took courage. A $100 million purse is on offer at the playoff finale; the difference between third and fourth, for example, is $1.5 million.

“I’ve just played so much golf,” Theegala said. “You spend so much time of your life staring down at the lie you have, the ball you have, and it just did not feel like a normal fairway bunker shot. It felt like some of the sand moved. At the end of the day I’m good with the ruling, and I think it’s very fair that I was assessed two shots.”

By Adam Zielonka