Jason Day Replaces Longtime Caddy Colin Swatton

Jason Day replaced caddie Colin Swatton, who has worked in the role for over a decade, though Swatton will remain Day's swing coach. 

"Sometimes the chemistry just doesn't work," Day said, per ESPN.com's Bob Harig. "He's been my coach since I'm 12. Obviously this is a very hard time for both of us with regards to we had a relationship for so long, my caddie for 11 years."

With Swatton by his side, Day has won 10 events on the PGA Tour, including the 2015 PGA Championship. He has also finished inside the top 10 of a major tournament on 14 occasions.

In September 2015, Day became the No. 1 golfer in the world—a status he regained in March 2016 after slipping down the World Golf Ranking.

Day's decision to replace Swatton comes in the midst of an underwhelming 2017 season.

He has yet to win a PGA Tour event and fallen to No. 9 in the world. Day appeared to get things back on track when he tied for ninth at the PGA Championship and then finished in a tie for sixth at the Northern Trust. Then he finished tied for 25th at the Dell Technologies Championship earlier this month.

Day said his "attitude is not good coming to the golf course" and that he didn't want to see his issues on the course spill over into his relationship with Swatton.

Luke Reardon will take over as Day's caddy for the BMW Championship and Tour Championship.