The Open Championship playoff format: What are the rules?

The Open Championship is wide open with 18 holes left at Royal Troon. 

Billy Horschel holds a slender lead but a cluster of players are in with a shout to lift the claret jug on Sunday at the final men's major of the year. 

That only means one thing: the chances of a playoff have risen significantly. 

But what is the playoff format?

Let us explain. 

The Open Championship is unlike a standard PGA Tour event and the playoff isn't a sudden-death contest. 

Instead, the R&A, who runs the major, employs a four-hole aggregate score playoff to determine the winner. 

At Royal Troon, players tied after four rounds will play holes 1, 2 and then the 17th and 18th. 

The low score among the players determines the winner. 

But what happens if the scores are tied once again?

Well, in that scenario the R&A goes to a hole-by-hole sudden death, playing the same holes again. 

The last time The Open winner was determined by a playoff was in 2015. 

American Zach Johnson prevailed over Marc Leishman and Louis Oosthuizen at the Old Course at St. Andrews. 

Players who have won The Open Championship in a playoff:

2010-Present:

• 2015: Zach Johnson defeated Marc Leishman and Louis Oosthuizen
• 2009: Stewart Cink defeated Tom Watson
• 2002: Ernie Els defeated Thomas Levet, Stuart Appleby, and Steve Elkington
• 1999: Paul Lawrie defeated Justin Leonard and Jean van de Velde
• 1995: John Daly defeated Costantino Rocca

1980-1989:

• 1989: Mark Calcavecchia defeated Greg Norman and Wayne Grady
• 1988: Seve Ballesteros defeated Nick Price
• 1984: Seve Ballesteros defeated Bernhard Langer and Tom Watson

1970-1979:

• 1975: Tom Watson defeated Jack Newton
• 1970: Jack Nicklaus defeated Doug Sanders

1950-1969:

• 1963: Bob Charles defeated Phil Rodgers
• 1958: Peter Thomson defeated Dave Thomas
• 1954: Peter Thomson defeated Bobby Locke

1940-1949:

• 1949: Bobby Locke defeated Harry Bradshaw
• 1933: Denny Shute defeated Craig Wood

1920-1929:

• 1927: Bobby Jones defeated Al Watrous
• 1925: Jim Barnes defeated Ted Ray and Archie Compston

1910-1919:

• 1911: Harry Vardon defeated Arnaud Massy
• 1910: James Braid defeated Sandy Herd

1900-1909:

• 1908: James Braid defeated Tom Ball

1880-1899:

• 1889: Willie Park Jr. defeated Andrew Kirkaldy
• 1876: Bob Martin defeated Davie Strath (in a controversial decision as Strath refused to participate in the playoff)

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