Question

1. I think the baseball club is more popular than the ping-pong club.

2. I think baseball club is more popular than ping-pong club.

3. I think Baseball Club is more popular than Ping-pong Club.

(Which expression is grammatical?)

Answer 1

1 and 3 are fine. 2 is incomplete. The word "the" is needed when referring to one particular club, but not by name.