Complex sentence: He was relatively injury-free until late in his career when an ankle problem saw him pull out of the March 2000 tournament and contribute to his demotion to the "juryo" division after the March 2001 tournament.
Split into simpler sentences: He was relatively injury-free until late in his career when an ankle problem caused him pull out of the March 2000 tournament. The injury continued to trouble him and contributed to his demotion to the "jūryō" division after the March 2001 tournament.