In chess, the clock is just as important as the pieces. If your time hits 0:00, the game ends immediately. But do you always lose? Not necessarily.
Even if you have a Queen, two Rooks, and are one move away from Checkmateβif your clock hits zero before you make that move, you lose.
This is the rule that confuses most beginners. To win on time, your opponent must have the potential to checkmate you.
Example Scenario:
Before digital clocks, chess players used analog clocks with actual clock hands. A small red flag was balanced near the 12 o'clock mark. As the minute hand approached the hour, it would lift the flag. When time officially ran out, the minute hand would drop the flag. Hence, "I flagged him" means "I made him run out of time."