Yes, when using it with a pronoun you need to use the preposition "di", while with a noun you can use it with an article or even without, if it's a first name.

• Contro DI lui (pronoun)
• Contro UN ragazzo (noun)
• Contro Luca (first name)

Yes, when using it with a personal pronoun you need to use the preposition "di", while with a noun you can use it with an article or even without, if it's a first name.

• Contro DI lui (personal pronoun)
• Contro UN ragazzo (noun)
• Contro Luca (first name)