Is tennis a proper noun or common noun?

The compound noun 'Table Tennis' is a common noun, a general Word for a type of game or sport.

A proper noun is the name of a person, place, thing, or a title; for example:

• Jike Zhang, ITTF No. 1 Ranked Men's Table Tennis Champion
• National Collegiate Table Tennis Association (NCTTA)
• Robbins Table Tennis Specialties, Inc., Clinton Township, MI