Complex sentence: In the ensuing shootout, Napier, who has realized he was set up, kills Eckhardt, but Batman also makes an abrupt appearance and, in a struggle, Napier is knocked into a vat of chemicals.
Split into simpler sentences: In the ensuing shootout, Napier, who has realized he was set up, kills Eckhardt. Batman arrives and, in a struggle, Napier is knocked into a vat of chemicals.