Jordan Spieth put himself in pole position at the 2015 Masters with a scintillating first round and in the process, he’s just given sportsbooks a lot of reasons to be concerned.

The fourth-ranked golfer in the world had everything go his way in the first round of the tournament, crushing Augusta on his way to posting an 8-under par score in the first 18 holes of the tourney. The 21-year old did set a record, becoming the youngest golfer to lead the prestigious major after the first round. While all of that is great for Spite’s narrative heading into the final three rounds of the event, sportsbooks who opened his chances at 10/1 odds are now pacing uncomfortably at the looming possibility that they could be in for a huge loss should Spieth end up winning the tournament.

First of all, taking bets in golf is always a risky proposition for sportsbooks. The odds on the golfers are like futures props in professional sports leagues, except that instead of having full seasons to adjust and modify odds, sportsbooks have three days to do it. It’s not uncommon for long shots to rise up the field and become favorites after a successful first round of a tournament. Sometimes, the odds evolve slowly as a golfer slowly moves up the ranks in the first three rounds of a tournament, putting himself in contention to win the tournament in the final round. Remember Webb Simpson? He won the 2012 US Open as a 50/1 long shot at the start of the tournament. Entering the final round, sportsbooks were still offering odds as high as 28/1.

Spite actually opened as one of the favorites so at least oddsmakers had the foresight to keep his odds in check. But what books didn’t expect was the rush of bets they took in on Spieth in the days leading up to the Masters. Of all the golfers with posted odds, Spieth was the most bet-on contender leading up the tournament. More bettors took a shot on the rising star than those who put money on tourney favorite Rory McIlroy, who finished seven shots back at 1-under par after the first round.