Disliking someone is one thing, but enough to the point that they would ban them is another. Besides, this could easily be controlled by only allowing "arena mods" to ban players from spawn temporarily. After that, a higher up could double-check to see if there was any sort of mistreatment, or change the temp to a perma-ban.

I think the smartest way, that someone already stated, is to have the account in question be monitored. The system flags them, and then someone can check where and how frequently their speed gets increased.

Aren't there any logs like ?
00:01:01 Player joins the spar queue
00:09:39 Player is flagged for probable action against the code of conduct