Spiking is the process of sending defensive troops to support an unoccupied village that you farm (be it a player or barbarian village). It is often considered the work of poor players, who don’t have the skills to beat a surrounding player outright, so use devious means. However anything goes in wartime and it can be a great tactic, if used properly.
Why is Spiking done?
This is done so that you can kill any other farmer’s troops who are farming this village; it is mostly used in early game, as a way of slowing down surrounding players so you can grow quickly. It also means you can gather more resources from that village, all the time whilst your troops stationed there are killing off the attacking troops, the resources are being accumulated. It is especially useful really early game, before your opponents get Light Cavalry, as until this point they will be farming with mostly defensive troops, and if their defensive troops hit aspiked village, they will suffer severe losses.
If used properly, it can be a great way to slow down good players early on, and give you a slight advantage over them, as well as giving you a while to farm the villages around you freely, as the other farmer will be left troop less.
If this tactic is used badly, the consequences can be disastrous, as a farmer may wipe all your defensive troops, and this makes you vulnerable to attack. Also, many players who are affected by spiked villages try to seek revenge, and if they start to spike villages as well, this will set you both back, and slow you both down.