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Greller caddied for the first time in 2006, according to Brian Costa of the Wall Street Journal, when he was watching U.S. Amateur Public Links Championship as a spectator and decided to hop across the ropes and caddie for a kid who was carrying his own bags.
He kept at it as something of a hobby, and in 2011 he found himself carry Spieth's bag in the U.S. Junior Amateur. When Spieth turned pro in 2013, he asked Greller to leave his real job and work for him.
Greller's job at the time: sixth grade math and science teacher at Narrows View Intermediate School in Washington.
Greller told Jason Sobel of the Golf Channel in 2013 that he initially intended to take a one-year sabbatical from school. But while watching the 2013 Masters, he decided that he didn't want to give up an opportunity to help Spieth win a green jacket one day.
He told Sobel:
"I loved what I did, but I was ready to try something different. Ellie, my wife, was watching the Masters with me in the spring. She said, 'If Jordan is winning the Masters in 10 years, are you going to be like, why didn't I pursue that?' I know I'd be kicking myself."
Greller's wife's question proved prophetic, although it didn't take Spieth 10 years to win the Masters, it took him two.
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Greller told the WSJ that he sees his job as more of a personality manager than a golf expert. As anyone who witnessed Spieth talking to his ball on nearly every shot at Augusta (even the good ones) can tell you, the 21-year-old expects a lot of himself.
"I just try to be a calming influence on him. He's very intense," Greller told the WSJ.
"We give each other a lot of crap," Greller told Sobel in 2013. "It's almost like a brother situation. We fight over the dumbest things, like sports."
What a special walk around Augusta National @TheMasters with Jordan, a lifetime of memories! Blessed to work for such a selfless person.
- Michael Greller (@michael_greller) April 13, 2015
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While we don't know the exact details of Greller's contract with Spieth, it's fair to say he's making more now than he could have teaching. According to Golf Digest's Undercover Pro, caddies on the modern PGA Tour typically get paid a base salary for $1,300-$1,800 per week with additional results-based bonuses. Traditionally, that bonus structure is 5/7/10 (5% of winnings for a made cut, 7% of winnings for a top-10 finish, and 10% of winnings for a tournament win). Although both the Undercover Pro and long-time caddie Kip Henley say caddies for top players are making more than that these days.
In the last 30 days Spieth has two second-place finishes and two wins, including the Masters (a $1.8 million prize), for a total of $4.1 million in winnings. Under the traditional rates, Greller stands to have made ~$375,000 in performance bonuses alone during that period.
Not too shabby for a guy who went to the Masters as a fan three years ago.