Anti Bot

Only players listed in the tab list under their own name.

Not players the tab list shows with 0 ping (on a local server, real players can show 0 too).

Not players with the kind of ID plugins give NPCs (real accounts never have one).

Not invisible players whose name is scrambled text.

Not players on a nameless team with a red name prefix (how some servers mark NPCs).

Only players that have touched the ground at least once.

Not entities with suspiciously high IDs.