Kusari-Gama is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Equipped creature has ": This creature gets +1/+0 until end of turn." Whenever equipped creature deals damage to a blocking creature, this Equipment deals that much damage to each other creature defending player controls. Equip (: Attach to target creature you control. Equip only as a sorcery.)