A hint: it is not a pest management crew or building workers. And not bugged NPC. Most probably you ran into a splasher. The general idea behind it's that if you reduce your magic bonus Strength enough your magic attack have an opportunity to deal no damage and vanish without even hitting 0. This gives you a opportunity to continuously attack your goal without slaying it, providing you experience per throw.
Splash technique is utilized by many RuneScape players to level up Magic while going afk, as doing it is almost as exciting as cutting a Yew Log. You don't need to pay much attention to the screen since rats around Lumbridge castle won't deal any damage. All you have to do is to click something on the screen or move a camera every 20 minutes, so that the game doesn't log you out.
How to start splash training? You have to edit your equipment installation and remove all of magic bonuses, such as your Magic Strength so you have negative magic stat. To do this you want to have one of two sets of the gear shown below. You want to equipment full plate collection with a kite shield and Green dragonhide vambraces (-10 Magic) or Cursed Goblin Staff.
IF you want to buy it ,we have many products like this ,you can access rsgoldfast