Sidebar widget depending on catergory

Can you have a sidebar widget only appear in the sidebar if a post from a certain catergory is selected?

Would i need a plug in to do this or is this a normal wordpress feature?

Example.

Let's say i had a soccer website and there was a post about Arsenal. If the person reads the post it would display an arsenal ad in the sidebar

If they read a post about chelsea it would display an ad for chelsea instead

etc etc