Complex sentence: By the third round, Lang, who is used to winning matches swiftly with knockouts in the early rounds, becomes increasingly furious over Rocky's taunts and quickly exhausts his energy trying to finish Rocky off with repeated knockout blows, which Rocky blocks or dodges.
Split into simpler sentences: By the third round, Lang, who is used to winning matches swiftly with knockouts in the early rounds, becomes increasingly furious over Rocky's taunts. He quickly exhausts his energy trying to finish Rocky off with repeated knockout blows, which Rocky blocks or dodges.