Complex sentence: Brennan announced his retirement on March 13th 2007, after he jumped into a section of the crowd housing Ulster supporters during a Toulouse v Ulster on January 21st, 2007 at Stade Ernest Wallon and struck Ulster fan Patrick Bamford.
Split into simpler sentences: Brennan announced his retirement on March 13th 2007, after an incident during a Toulouse v Ulster match on January 21st, 2007. Brennan jumped into a section of the crowd housing Ulster supporters at the Stade Ernest Wallon and struck Ulster fan Patrick Bamford.