The first two days of the Ryder Cup sees four sessions of golf, with eight players from both teams being named in each session.
Generally, players will play at least one match on Friday and Saturday, though occasionally, a player sits an entire day, as Rasmus Hojgaard and Ben Griffin did this year, missing both of Saturday's sessions. At the 1999 Ryder Cup, Andrew Coltart, Jarmo Sandelin and Jean Van de Velde sat both days, making their first appearances on Sunday, with all three losing.
On Sunday, however, all 12 players play singles matches, though there is a potential exception.
If a player on either side is injured and unable to play on Sunday, the captain of the opposing team has a pre-selected name to put forward to sit out the singles match. The match would be halved.
Within an hour of the end of play on Saturday, both captains put a name in an envelope, with a player they would remove on Sunday.
It's a rule that's only come into play twice. First in 1991, when US player Steve Pate, who'd been injured in a car accident earlier in the week, ruled himself out of the Sunday, with David Gilford missing out for Europe.
In 1993 at The Belfry, Lanny Wadkins volunteered himself, making captain Tom Watson's life much easier when Sam Torrance pulled out of Sunday with a foot injury.
It may be that the envelope needs to be unsealed again this year, with Viktor Hovland pulling out of the Saturday four-balls with a neck injury.
