Complex sentence: Throughout his career, Henman would be a noted grass specialist, not becoming truly comfortable on clay and hard court before the end of his career, when in 2004 he reached the semi-finals in both the French and US Open.
Split into simpler sentences: Throughout his career, Henman would be a noted grass specialist. Henman did not become truly comfortable on clay and hard court before the end of his career, in 2004, when he reached the semi-finals in both the French and US Open.