[Wliu]

You'll have to create a new global array, something like new shieldsLeft[MAXPLAYERS + 1]. Then somewhere reasonable (CheckItems, MakeNotBoss, something like that) assign however many shield hits you want to everyone.

Then change this bit of code to the following:

if(shield[client] && shieldsLeft[client] && damage)
{
    shieldsLeft[client]--;
    if(!shieldsLeft[client])
    {
        RemoveShield(client, attacker, position);
    }
    return Plugin_Handled;
}

And finally, make sure to reset shieldsLeft to 0 at the end of each round (or beginning).