"As it happened" indicates that the report is going to give you a step-by-step description of the important moments of the match. The link doesn't seem to take me to a match report, but I would expect an "As it happened" report to look something like this (but longer!):
08:47 West Ham have a shot on goal but the keeper knocks it away.
15:22 Stoke substitute Jerry Smith for Terry Jones.
25:32 West Ham score from a corner kick.
45:00 1-0 to West Ham as the ref blows for half-time.
62:17 Jefferson's overhead kick hits the post.
78:02 Stoke's James Coburn gets a red card. Stoke are down to ten men.
90:00 We've got four minutes of extra time
94:00 That's that! West Ham win 1-0, giving them their sixth win in seven games.