[[XST]O_x]

I'd suggest you moving to dcmd to make commands with parameters.
But if you insist:

pawn Code:

public OnPlayerCommandText(playerid, cmdtext[])
{
    new cmd[256];
    new tmp[256];
    new idx;
    cmd = strtok(cmdtext, idx);
    if(strcmp("/cuff", cmd, true) == 0)
    {
        tmp = strtok(cmdtext,idx);
        if(!strlen(tmp)) return SendClientMessage(playerid,0xFF0000FF,"USAGE: /cuff [playerid]");
        if(!IsPlayerConnected(strval(tmp))) return SendClientMessage(playerid,0xFF0000FF,"Player is not connected");

        TogglePlayerControllable(strval(tmp),0);
        GameTextForPlayer(strval(tmp), "~y~ hand cuffs!",2500,3);
        return 1;
    }
    return 0;
}