Complex sentence: In his final bout, he demonstrated his exceptionally hard punching power by staggering the powerful George Foreman, but was unable to capitalize on it; again showing himself deficient at basic self-protection, Cooney suffered a devastating second-round knockout that ended his career.
Split into simpler sentences: In his final bout, Cooney demonstrated his exceptionally hard punching power by staggering the powerful George Foreman, but was unable to capitalize on it. Showing a deficiency in basic self-protection, Cooney suffered a devastating second-round knockout that ended his career.