They usually have about 150 participants on round 1. They might put them foursomes if they all start on the first tee. Most of the time they split the tees to keep the groupings to two or three: half the people start on the first tee and the other half start on the 10th tee (they put an asterisk or arrow to indicate this on the scoreboard). They flip the starts on round 2.
They will also do morning starts and afternoon starts, and then flip that on round 2. Sometimes they even have multiple courses and start one set on one course and the other set on the other, and then flip that on round 2.
Then they do the cut. They try to put the cut line so that about 75 players advance to round 3, plus or minus based on ties. At that point, they group people based on cumulative strokes, with the leaders going last. They group the players separately for rounds 3 and 4 based on cumulative strokes each day.
If there are weather delays they may change this. If play is called on round 3 so that they have to complete it on the morning of day 4 and then start round 4 later in the morning, they might keep the groupings as is for round 4 to minimize downtime and confusion depending on the length of the make-up time.
-PJ
Usually the top 70 players and ties, or the ten-shot rule…