Here's why:

* Oxidation: Sulfur (S) goes from an oxidation state of 0 in elemental sulfur to +4 in sulfur dioxide (SO2). This is an increase in oxidation state, meaning sulfur is oxidized.

* Reduction: Chlorine (Cl) goes from an oxidation state of +5 in potassium chlorate (KClO3) to -1 in potassium chloride (KCl). This is a decrease in oxidation state, meaning chlorine is reduced.

Therefore, the reaction involves both oxidation and reduction, making it a redox reaction.

Let me know if you'd like a more detailed explanation of oxidation states or want to explore other types of chemical reactions!