SQL Server 2017 | db<>fiddle

CREATE TABLE dbo.Matches(DateField DATE,HomeTeam varchar(100),AwayTeam varchar(100));

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INSERT INTO dbo.Matches VALUES ('2018-08-10', 'Man United', 'Leicester'), ('2018-08-11', 'Bournemouth', 'Cardiff'), ('2018-08-11', 'Fulham', 'Crystal Palace'), ('2018-08-11', 'Huddersfield', 'Chelsea'), ('2018-08-11', 'Newcastle', 'Tottenham'), ('2018-08-11', 'Watford', 'Brighton'), ('2018-08-11', 'Wolves', 'Everton'), ('2018-08-12', 'Arsenal', 'Man City'), ('2018-08-12', 'Liverpool', 'West Ham'), ('2018-08-12', 'Southampton', 'Burnley'), ('2018-08-18', 'Cardiff', 'Newcastle'), ('2018-08-18', 'Chelsea', 'Arsenal'), ('2018-08-18', 'Everton', 'Southampton'), ('2018-08-25', 'Round3Example_1', 'Round3Example_2')

14 rows affected

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;WITH CTE AS ( SELECT DateField, CASE WHEN DATEDIFF(day,LAG(DateField) OVER(ORDER BY DateField),DateField) > 3 THEN 1 ELSE 0 END as newround, Hometeam, AwayTeam FROM dbo.Matches ) SELECT Datefield, HomeTeam,AwayTeam, SUM(newround) OVER(ORDER BY DateField) + 1 FROM CTE;

Datefield	HomeTeam	AwayTeam	(No column name)
10/08/2018 00:00:00	Man United	Leicester	1
11/08/2018 00:00:00	Bournemouth	Cardiff	1
11/08/2018 00:00:00	Fulham	Crystal Palace	1
11/08/2018 00:00:00	Huddersfield	Chelsea	1
11/08/2018 00:00:00	Newcastle	Tottenham	1
11/08/2018 00:00:00	Watford	Brighton	1
11/08/2018 00:00:00	Wolves	Everton	1
12/08/2018 00:00:00	Arsenal	Man City	1
12/08/2018 00:00:00	Liverpool	West Ham	1
12/08/2018 00:00:00	Southampton	Burnley	1
18/08/2018 00:00:00	Cardiff	Newcastle	2
18/08/2018 00:00:00	Chelsea	Arsenal	2
18/08/2018 00:00:00	Everton	Southampton	2
25/08/2018 00:00:00	Round3Example_1	Round3Example_2	3
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