In Flagman, the titular Flagman stands in the centre of the screen and the player presses the buttons for the numbers 1 to 4 in the same sequence as the Flagman.

As in many Game & Watch games, there are two modes, GAME A and GAME B. In both modes, the game ends after the player has used their three lives, and the maximum score is 99 points. However, the game content differs greatly between GAME A and GAME B.

GAME A is a test of memory, where the Flagman performs a sequence of numbers and the player must replicate the sequence by pressing the same numbers in the same sequence. If the player presses the wrong number in the sequence, or doesn't press a button within five seconds, they lose a life. The Flagman will add an extra number to the sequence each time the player successfully completes a sequence. GAME B is a test of reflexes, where the Flagman shows a number and the player must quickly press the number button within two seconds. More points are awarded depending on how quickly the button is pressed.