Game that's the hidden theme of this puzzle

• Game that's hard to lose
• Game with losing lines in 18-A, 28-A and 48-A
• Two-person pencil-and-paper game
• Theme of the puzzle
• Match game?
• XXX activity
• Simple game for two
• Drawing game, often?
• It's rarely won

Wikipedia Word definitions in Wikipedia
redirect Tic-tac-toe