How To Spot A Hacker
These are just a few of the many ways a player might be able to identify if another player is hacking in-game.

One of the dead giveaways is when they have blocks moving around them as they are sprinting but they're standing still. It's somewhat hard to see, but you can see gray blocks moving around him as he is sprinting, but he's standing still.​

This hack/cheat enables critical hits for the hacker no matter what/when they hit. This means if you have a diamond sword and the hacker has a stone sword, they will most likely kill you with criticals.

This hack/cheat enables sprint to be faster, and unlimited. If you see someone running faster then normal, they are most likely using this.

This hack/cheat enables the user to hit an opponent from any direction. This allows a user to stand still and hit in a 360 degree space without even touching their mouse. If a user spins around and immediately hits you when they are not looking at you this is most likely the ambit.

This hack/cheat enables the user to "derp". This basically lets the players body jump around or spin in crazy ways. Extremely visible and very idiotic for a hacker to use.

Both of these will basically let you climb up walls and easily step over blocks.
These are the main cheats/hacks used on the servers.