Logic behind multiplayer melee attacks?

I have spent quite a bit of time recently building a very basic multiplayer game from one of the uLink demos (Snowbox) and feel I have a pretty good understanding of how it all fits together and works as a whole.

As the player model I am using (City Guard from Asset store) has a spear, I would like to go ahead and try creating some melee attacks now where players can damage one another. Unfortunately despite quite a lot of searching on the topic, I am clueless how to handle this in terms of a multiplayer game.

Can anyone shed some light on how this should/could be addressed?