Complex sentence: Knowing that Cole is determined to bring Bragg back to hang, Ring and Mackie (with the sherriffs help) free Bragg and challenge Cole and Hitch to a gunfight.
Split into simpler sentences: Knowing that Cole is determined to bring Bragg back to hang, Ring challenges Cole. With the sheriff's help, Ring and Mackie free Bragg and challenge Cole and Hitch to a gunfight.