[DavidBilla]

pawn Код:

public OnPlayerTakeDamage(playerid, issuerid, Float: amount, weaponid)
{
    new Float:HP;

    GetPlayerHealth(playerid, HP);
    if(weaponid == 25)
    {
        SetPlayerHealth(playerid,HP-10.0);
        return 0;
    }
    return 1;
}

I guess this'll do what you wanted.