A match sequence is a game mechanic that appears at the end of a game of pinball. It often takes a rounded up number from the end of a players score and compares it to a random set of numbers. If the players number matches the random number the player will be awarded a free game. Many pinball machine play a very loud "knock" sound to attract the attention of nearby individuals that the player has won the free game.
Often times, depending on the table, operators of the table can set the percentage of times a free game is won.