Complex sentence: A highly technical boxer, Tunney had a five fight rivalry with Harry Greb in which he went 3-1-1, knocked out Georges Carpentier and defeated Jack Dempsey twice; first in 1926 and again in 1927.
Split into simpler sentences: A highly technical boxer, Tunney had a five-fight rivalry with Harry Greb in which he won three, drew once, with one no-contest. He also knocked out Georges Carpentier and defeated Jack Dempsey twice; first in 1926 and again in 1927.