Fields in golf tournaments are larger than the total number of places paid out. A cut is used to determine which players will make it to play into the weekend and, in doing so, will qualify to receive a check from the tournament based on their place of finish.
The Opening Rounds
All players that qualify for or given a spot in a tournament are permitted to play the work week rounds: 18 holes on Thursday and 18 holes on Friday--in the case of most 72 hole tournaments. These first two rounds are used to rank the players by score headed into the weekend. These rounds feature pre-assigned groups of three players, in most tournaments, and the players are not re-paired to reflect leader board position after day one.
The standard cut line for a PGA event after two rounds is the score of the 70th lowest scoring professional. Any players that finish with that score or better are considered to have made the cut and continue play in the weekend rounds, unless the number of players in the tie merits further tie-breaking.
More than 78 Qualifiers
When more than 78 players make the cut, it is necessary to apply further tie breaking procedures to determine which players get to play in the remaining rounds. In this case, the next highest score below that of the 70th player is used, and it is determined how many players would make the cut should that be the line. Whichever number is closer to 70, either the number of players at the original line or the number of players at the lower line, is used as the cut for which players make the weekend, meaning less than 70 players can potentially qualify. Should a cut like this occur, the players that made the 70th-place tie cut but were eliminated anyway receive a check but do not play further.
Should the higher cut line be used following 36 holes, and more than 78 players qualify for the next round, a second cut occurs after 54 holes. This cut uses the same procedures (top 70 and ties). While this cut does not determine if the players receive money for their performance, it does determine which players are permitted to play the next, usually final, round.
10 Stroke Rule
Some events utilize a 10-stroke cut rule, under which any player within 10 strokes of the leader after two rounds is permitted to make the weekend, even if the player ranks worse than 70th. This is primarily used in major tournaments, where the course is very difficult and a player who goes out and shoots a score in the mid-60s can climb through the field quickly.