The player only sees 

Disconnect: Banned

The player does not see a reason for the actual ban

P4R4

The player only sees 

Disconnect: Banned

The player does not see a reason for the actual ban

On Rust if the native ban system is used they won't see the reason. Last I checked Oxide/uMod runs the CanUserLogin hook after the native banlist is checked. I assume that's the same for the other games as well. If you want to see the reason disable the native ban method.

Native bans is completely disabled on all my servers as they don't support Temp bans.