;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;