Conversation so far:
When was the Alf-Inge Haland incident with Roy Keane?
The Alf-Inge Haland incident with Roy Keane was in 2001
What happened during the Alf-Inge Haland incident in 2001 with Roy Keane?
Roy Keane made headlines again in the 2001 Manchester derby, when five minutes from the final whistle, he was sent off for a blatant knee-high foul on Alf-Inge Håland
How did the Alf-Inge Haland incident where he was sent off for a blatant knee-high foul on Alf-Inge Håland affect Roy Keane's career?
Roy Keane initially received a three-match suspension and a £5,000 fine from The Football Association, but further punishment followed after the release of Keane's autobiography in August 2002
Was there a lot of controversy about the Alf-Inge Haland incident?
The Alf-Inge Håland incident with Roy Keane was seen by many as an act of revenge
Why was the knee-high foul by Roy Keane seen as revenge in the Alf-Inge Haland incident?
An admission that the tackle was in fact a premeditated assault, it left the FA with no choice but to charge Roy Keane with bringing the game into disrepute.

Question: Why was he angry with Haland?
Self-contained rewrite: Why was Roy Keane angry with Haland in the Alf-Inge Haland incident?