I have listened to the parliament speech of the president of country XYZ once, and from that I must conclude that he is a lousy speaker. Which fallacy is committed in the above statement?

Drawing a sweeping verdict from a single instance is a hasty generalisation.

The speaker heard just one parliamentary speech of the president.

From that lone sample a general judgement that he is a lousy speaker is drawn.

One instance is far too small a sample to support such a general claim.

Generalising from insufficient evidence is the fallacy of hasty generalisation.