Michael is right. If you want to say it was a bad defeat the adjective needs to come in front of the verb. Juventus were (the team is made of many players and hence plural) badly beaten by Barcelona. Or 'Juventus lost (badly) to Barcelona. We have lots of ways to express a terrible defeat but I don't if they are appropriate for the game yesterday given it was quite close. 3-1 isn't a bad defeat. Anyway let's go with the premise that it was a bad defeat. Juventus were completely outplayed by Barcelona. (This says nothing about the result, just that Barcelona were the much better team.) Juventus were thrashed by Barcelona. (Really common in the UK when it is a bad defeat.) Juventus were annihilated by Barcelona. Juventus were destroyed by Barcelona. Barcelona beat Juventus convincingly. Barcelona beat Juventus easily. There are so many ways to describe sporting events, these examples are no by means the only ways to do so.

You wouldn't say "the Barcelona" just "Barcelona" While I am not British, I can say that "Juventus was beaten by Barcelona badly." is probably not what you are trying to say as it seems to imply that Barcelona did a poor job of beating Juventus. Having seen and enjoyed the game myself, I would say that Juventus were badly beaten by Barcelona.