In the past century there haven't been many opportunities for a member of the Swiss Guard to need to use their halberd. From our arbitrary cutoff date of 1914 until 1929, there was some level of animosity between the Vatican and the surrounding Italian state. Rome was declared the capital of the new Italian state in 1861, and that same year saw the Papal States lose most of its territory. The papacy lost Rome in 1870 and Pius IX declared himself a "prisoner of the Vatican." (prigioniero del Vaticano) The period from 1861-1929 saw varying levels of mutual antagonism between the papacy and the newly unified Italian government--but no outright violence. The papacy didn't have the troops to contemplate an armed recovery of its (former) territory, and the Italian state had no desire to wipe out the last vestige of papal territory.

So, starting with 1914, we have Benedict XV. His diplomatic efforts during WWI were seen fairly favorably in Italy and there was no confrontation between the two bodies during that time. His successor was Pius XI (elected in 1922), who had varying levels of conflict and attempts at accommodation with Mussolini's government, but again no armed conflict. In 1929 the Lateran Accords were signed between those two entities, creating the new nation of the Vatican City. Article 3:

Italy recognizes the full ownership, exclusive dominion, and sovereign authority and jurisdiction of the Holy See over the Vatican as at present constituted, together with all its appurtenances and endowments, thus creating the Vatican City, for the special purposes and under the conditions hereinafter referred to

Article 24 made strict neutrality in foreign affairs a treaty obligation of this new nation

In regard to the sovereignty appertaining to it also in international matters, the Holy See declares that it desires to take, and shall take, no part in any temporal rivalries between other States, nor in any international congresses called to settle such matters, save and except in the event of such parties making a mutual appeal to the pacific mission of the Holy See, the latter reserving in any event the right of exercising its moral and spiritual power.

The Vatican City shall, therefore, be invariably and in every event considered as neutral and inviolable territory

So, from 1929 until the present (the treaty is still in force with minor changes) the Vatican has been a neutral country. This leaves only one period of time and another moment where the Swiss Guard came into potential conflict. The period is WWII. The Swiss Guard--along with other formations like the Palatine Guard and Noble Guard--helped secure Vatican territories during that massive conflict. While they did clash from time to time with Italian and later German forces, I don't know of a time when the conflict became armed--halberds or otherwise. With many Vatican properties housing refugees from the Italians or Germans, it wasn't the force of arms that kept them secure as there simply wasn't enough men in the papacy's employ to keep the fascists out if they made a real attempt to force entry. Instead, a lack of desire for an outright attack on the Vatican (and by extension, the papacy) for a number of reasons kept the Vatican's territory largely respected during the war. (The Vatican was hit by a single Edit: new evidence says between one and five German Edit, typo: Italian bomb during the war as well as a single British bomb, though the identity of the bomb I attribute to the British may have been American or even Italian as that case isn't 100% clear. A book came out in 2010 on the subject, but I haven't read it because I didn't know it existed until recently and it is in Italian which I struggle with).

The moment I mentioned would be the 1981 attack on John Paul II, but no halberds were used in his defense. The gunman tried to flee after taking his shots, but was physically grabbed by a number of people nearly instantly--the halberds had no chance to come into play.

So it is difficult to prove a negative, but I know of no instance in which the halberds have drawn blood in the past century. You'd have to go back to at least 1870 to find armed conflict between the papacy's forces and another government.