 How the clock works in football can be a little confusing at first. Not only is it not like rugby where the clock runs all the time, and it's not even like hockey or basketball where the clock stops when play stops, sometimes it stops, sometimes it keeps going, it's chaos. So let's try to make it slightly less confusing. A football game will consist of four 15 minute quarters. These are divided into two halves. At the start of the second and fourth quarters, the teams switch directions, but the team with the ball keeps the ball. At the start of the third quarter, the team who kicked off to start the game will receive a kick off of their own. The game clock will stop when an incomplete pass is thrown, when there's a penalty, when a team scores, after an exchange of the ball like on a kick off upon their turnover, and when a player is injured. The exception to an injury being if the player is hurt with less than two minutes to go in either half, his team will be charged with a timeout. This will prevent players from faking an injury just so that they can stop the clock. One of the most common ways for the clock to stop will be when a player with the ball runs or is pushed out of bounds, but it will keep ticking when a player is tackled on the field in bounds. This usually only becomes an issue late in the second and fourth quarters when a team is trying to score before time expires. You may even see a player run out of bounds on purpose so he can stop the clock without his team having to call timeout. In college football, the clock will also stop when a team gets a first down so that they can move the first down markers up. Once they move, the clock will restart. In the NFL, the clock keeps moving and they just make the chain crew run. At the end of any quarter, if a play is in progress when the clock hits zero, the play is allowed to continue until it ends. So even if you snap the ball with just one second remaining, however long the play takes is irrelevant. For this reason, if the defense commits a penalty on a play when time has expired, then the offense will get a free, untimed play, otherwise the defense could just do whatever they want on that play. The two minutes left in a half. This is in both the second and the fourth quarters. There is a timeout called the two minute warning where the clock stops just because. The two minute warning began before the clock was on the scoreboard and was just kept by the referee so it was a notification to both teams that the game is almost over. Nowadays though, with the official clock on the scoreboard, some say the two minute warning helps to build suspense at the end of the game. Others though say it's just an excuse so that there can be an extra commercial break. Each team will get three timeouts per half. This can be called at any point between plays, although one team can't call two timeouts in a row unless a play has taken place in between. If you don't use all of your timeouts, you can't roll them over to the second half. Sorry, this isn't Verizon. Kind of like a shot clock in basketball. The play clock will start at the end of each play and then run for 40 seconds. This is whether or not the game clock is moving. The offense has that 40 seconds to snap the ball again. You'll usually see the play clock somewhere on the screen if you're watching a game on TV. If the offense doesn't snap the ball in time, they'll get a five yard penalty for delay of game. In some situations, like after a penalty or a timeout, the offense will only have 25 seconds to snap the ball rather than the full 40. If you see a referee moving his arm like a windmill or like a third base coach waving a runner home, that means he's winding the clock, which is just the signal to start it again. The clock can play a big part in a close game. Teams that take a big lead in a game early will generally try to run the ball more in the past because they have a higher likelihood of getting tackled in bounds and therefore keeping the clock moving. Spiking the ball does not involve alcohol. It means that the quarterback is going to take the snap and immediately throw the ball into the ground. This is considered to be an incomplete pass, so it will cost the offense a down, but as is the case with all complete passes, the clock will stop and it won't cost the team a timeout. On the flip side, the quarterback can also receive the snap and just kneel down. This is considered a running play with the ball down in bounds, so the clock will keep on ticking. Usually this will happen when a team is winning and there's just a few minutes left. Taking a knee will allow them to run the clock out without taking the risk of handing off and potentially risking a fumble.