If you are constructing an argument then a definition of sport would be a good place to start '
an athletic activity requiring skill or physical prowess and often of a competitive nature' then you can clearly justify a set of criteria and argue how table tennis meets those criteria.
Athleticism and Physical Prowess - show fitness programmes and physical training involvement in table tennis, the physical nature of an intense match or of multiball training.
Skill Requirement - Show various amazing shots, different spins and implementation of physics into the game, spin, acceleration concepts and theories and demonstrate the amount of analysis of tactics and technique required to become a great player.
Competitive Nature - Perhaps you can outline celebrations by players such as Zhang Jike to outline the release of competitive tension upon victory or examine the fact that in a 2 serve - 11 point game it's all or nothing and every point is fought for.
That's a good place to start, hope it helps