Complex sentence: He left in 2004, joining Paul Merson as assistant manager at Walsall but resigned in January 2005 after a 5--0 defeat at the hands of Colchester United almost cost Merson his job.
Split into simpler sentences: He left in 2004, joining Paul Merson as assistant manager at Walsall. He resigned in January 2005 after a 5--0 defeat at the hands of Colchester United, which almost cost Merson his job.