[Kaliber]

Like this:

PHP код:

static stock CheckMultipleName(const name[])
{
    new bool:x,i=GetPlayerPoolSize()+1,n[MAX_PLAYER_NAME];
    for(; --i!=-1;)
    {
        if(!GetPlayerName(i,n,MAX_PLAYER_NAME)) continue;
        if(!strcmp(n,name,true))
        {
            if(x) return 1;
            x=true;
        }
    }
    return 0;
}
//Then OnPlayerConnect or somewhere else:
new name[MAX_PLAYER_NAME];
GetPlayerName(playerid,name,MAX_PLAYER_NAME);
if(CheckMultipleName(name))
{
    return Kick(playerid); //Here the name was multiple found
}