Possible Clues:

• Tic-tac-toe loser
• Losing tic-tac-toe row
• Losing line in tic-tac-toe
• Blocked tic-tac-toe line
• Losing tic-tac-toe line
• Losing line
• It's for naught in noughts-and-crosses
• Tic-tac-toe line
• Tic-tac-toe failure
• Noughts-and-crosses loser