Translation:That player needs to change his nickname.
Kaŝi comes from "cacher" in French : so this is a "hiding name" litterally. So pseudonym is best assumption. Nickname is : alnomo or kromnomo that is "additional name" or "petolnomo" aka joking name http://vortaro.net/#nomo http://reta-vortaro.de/revo/art/nom.html#nom.al0o * https://fr.wiktionary.org/wiki/petolnomo#eo
I can't remember where I heard it, but I was told that "devi" implies a need put upon someone from outside sources, whereas "bezoni" implies a need from within.
for example "Mi bezonas manĝi" implies that my body is telling me I need to eat, where as "Mi devas manĝi" implies that something else is telling me to eat (for example "I have to eat [because it is getting late]").
don't know if that helps, but that's the distinction I have been using.