From a purist standpoint, the flySpeed tag should never be messed with in MobArena, because simply turning off flight should be enough. It is likely that the flySpeed tag was originally included to cull "cheaters" who somehow managed to activate flight in the arena anyway, but this isn't really MobArena's responsibility and can very probably be handled by other means of cheat prevention in WorldGuard regions or the like. By not touching the flySpeed tag, it makes it much easier for server owners to recover from crashes where the leave steps aren't executed, leaving players "locked in the air" when they try to fly. Closes #509 since this "fix" was the reason that feature request was made.
MobArena

MobArena is an arena-style minigame for Spigot-based Minecraft servers
Getting Started
If you don't want to compile the plugin yourself, grab a release artifact from one of these two sites:
The wiki here on Github should have all the information you need to get started using the plugin.
Getting Help
If you run into problems or need help with something, feel free to hop on the MobArena Discord server to have a chat: Instant Invite
Remember, though, that this communication channel is idle chat, which means you likely won't get a response immediately. It could take anything from a couple of seconds to a day, but your message will be seen.
Contributing
Found a bug, got a suggestion, or want to dig into the code base? There are many ways to contribute to the project!
Get started here: Contributing