Okay, I'm not sure whether these people were abusing a glitch, or whether they were hacking, but I'm leaning toward abusing a glitch. I have no proof for this one, but at least I learned not to record and share my screen over Skype at the same time. It completely messed up the audio, and the video wasn't much of a video, and more of three screenshots, which is very suspicious, which is why I decided not to send it in altogether.
The people's usernames were casspi18 and Caspiiian who I saw doing this, and one of them is on the top kills section of KitPvP. Anyway, after I saw that they were killing each other five times every ten seconds, I peaked over the edge of the KitPvP spawn and, at the moment, they weren't doing anything, and chat wasn't being spammed anymore. I continued to watch, and I saw that one of them spawned a horse from one of their kits, and the other person began killing them over and over, and they weren't even respawning or coming back to spawn. They stayed in the same location on their horse, and they kept getting kills.
This could all be wrong, but if you could check this out, that would be awesome. Thanks!
You can call me Bean... :D