There are two teams, the number of players is not important as the players continuously rotate positions (4 on each team is probably a good goal so that it isn't too hectic and each player gets enough 'rest'). Use a beer pong table set up as pictured above. Each team sets up a reverse 10-cup beer pong triangle offset to one side of the table, these are the yardage cups. Cups should be filled enough not to get knocked over by ping pong balls, and each row should be filled progressively higher with 1 being lowest and 4 highest. I recommend rows 1 and 2 not be filled as high as a beer pong cup, and rows 3 and 4 slightly higher. A lone cup opposite the triangle, the Hail Mary Cup, is to be filled much higher, approximately halfway (or more if you like). The three flip cups at midfield will be used for linemen play and will be used and reset every play.
In addition to cups and ping pong balls, you should have a triangle football (a paper one, or a FIKI) to mark where the ball is currently placed on the field, and to use for the kicking game. You will also need some means to keep track of down and distance, score, and any stats you want, perhaps a dry erase board, chalk board, paper, or maybe you think you can go by memory. . .
This game is done play by play with the same rules for yardage and scoring as football, while yardage gained per play is simulated by drinking game. There are two phases to each play: blocking and yardage. Flip cup is played as blocking, determining how many balls will get to be thrown for yardage. Each cup flipped is a ping pong ball to throw. One player on each team will act as the line each turn, and one player on each team will be designated to throw for yardage each turn (QB and MLB if you want a title). The teams will rotate players through these two positions throughout the game. Each offensive yardage cup made per play will add a specified number of yards to that play, and each defensive yardage cup made per play will subtract a specified number of yards from that play. The yards per cup will depend on if the play is a run or a pass.
Before each play starts, the offense must call whether the play will be a run or a pass. If it is a run, the offense automatically gets 2 balls to throw for yardage, plus whatever the lineman flips, a maximum of 5. If it is a pass, the offense gets no guaranteed throws, only what the lineman flips, a maximum of 3. However, each yardage cup is worth more for a pass than a run. In either case, the defense will only throw what its lineman flips, a maximum of 3. The following table shows what the yardage cups are worth:
Once the play is called, the linemen line up across the table from each other with 3 cups in front of each of them. The blocking is a one-on-one game of flip cup. Each player starts simultaneously, must drink a cup, place it on the edge of the table upright, flip it in the air trying to land it upside down on the table. He must continue flipping the cup until he successfully lands it before moving on to the next cup. When one player flips his third cup, the other player must stop. The winning lineman has gained three balls for his teammate to throw for yardage on that play, whatever the losing lineman has flipped in the same time is how many balls he has gained for yardage. A tie may occur, in which case each team gains three balls to throw for yardage.
Once the blocking is finished, the offense will throw for yardage first. This will be 2-5 throws on a run, and 0-3 throws on a pass. Once the offense is finished throwing for yardage, the defense throws all its balls. All yardage made by the offense is added up, then all yardage made by the defense is added up and subtracted from the offense's total, the result is how many yards were gained on the play. All cups made will remain on the table until the throws are complete. Once the throwing is complete, all made cups must be drank, filled, and replaced by the team with cups made in front of them. There are exceptions to this play format, outlined below.
If the defense makes the 'sack' cup on a pass play, the QB was sacked before getting the throw off, so any positive yards are immediately wiped out, and the play is a 5 yard loss. If the defense makes the sack plus other yardage cups, those yards tack on to the 5 yard sack. It may seem unfair that the offense's yards don't count, but this is simply a bonus that you don't get in real life. You get to see what WOULD have happened had the sack not been made, real football can't claim that.
If the offense makes the maximum possible yardage throws, the thrower then gets a shot at a breakaway for an immediate touchdown. What is meant by 'maximum possible' is if 5 cups are made on yardage throws for a run, or 3 cups are made on yardage throws for a pass. It does not mean that if you only get one ball to throw, but make it, you get a chance at a breakaway. Your lineman must flip all 3 cups to first give you a chance at a chance for a breakaway. If you get a chance at a breakaway, the current thrower gets one shot at the Hail Mary Cup. If he misses, the play continues as normal and the defense shoots any balls they have for yardage. But if he makes it, it is an automatic touchdown, the defense gets no rebuttal (that is the lineman's fault for allowing the offensive lineman to flip all 3 cups), and must drink the cup.
If the offense makes zero yardage cups, the defense gets a shot at a turnover. If it is a pass, and the offensive lineman flipped no cups, the defense gets a shot at an interception before shooting for yardage. If it is a run, the offense will still have at least two shots for yardage, but if they miss all shots, the defense gets the shot at a turnover. It does not matter if the defense has zero balls to throw for yardage, if the offense takes and misses all yardage shots, there is a chance for a turnover. If the defense has a chance at the turnover, the current thrower gets one throw at the Hail Mary Cup. If he misses, the play continues as normal and he shoots whatever yardage balls he has. If he makes it, the offense drinks it and he has either recovered a fumble or made an interception, depending on whether it was run or pass. If the turnover is an interception, the defensive thrower then gets to try for return yardage. However many balls he had to throw for defensive yardage is how many he gets to throw for return yardage in this case, but he must bounce return throws in, instead of throwing. The yardage in this case is the same as an offensive pass: rows 1, 2, 3, 4 are worth 5, 10, 15, 20 yards respectively. If the defender has all three yardage throws, and makes them all, then the breakaway rule applies to him.
The offense has a chance to prevent a turnover if it chooses. On the offensive thrower's last throw, if he has not made any yardage cups yet, he may decide to forego the last throw, which effectively means he is tucking and going down with the ball rather than risking the turnover. In this case, the defense throws as normal, all yardage cups made to go for a net loss of yards. Of course, the offense must have a ball to throw in order to tuck, it cannot tuck if on a pass the lineman does not flip any cups. If on a pass the lineman only flips one cup, the thrower may decide not to throw at all and prevent a shot at a turnover.
Instead of simply calling run or pass, the offense may try a Hail Mary. In this case, there is no blocking phase to the play. Each offensive and defensive thrower get one throw at the Hail Mary Cup. If both players miss, or if both players make, it is an incompletion. If the offense makes it and the defense misses, it is a touchdown. If the defense makes it and the offense misses, it is an interception. Any cup made must be drunk by the opposing team. You may want to come up with some arbitrary limits to how many times or how often you can run this play, so that the game doesn't get ridiculous (MORE ridiculous than it already is, anyway).
After any play in which the net yardage gained puts the offense in or through the end zone, this is a touchdown (in case you never watched actual football). For the extra point, simply flick your triangle football from mid-table into goalposts (or fingers held up as a goal posts).
At the beginning of the game or half, or after a score, perform a kick off. For this the kicking team shall slide the triangle football as if playing table football. If it goes out of bounds, it is a penalty as in real football, and possession starts at the 40 yard-line. If it goes into or through the end-zone, it is a touchback. If it lands in play, where it lands is where the receiving team catches it. In this case, the receiving team will have a chance for return yards. It is like an interception return in that the balls must be bounced in and the rows 1-4 are worth 5, 10, 15, and 20 yards. The returner will get one throw. If it goes in the back cup, he gets another shot. If it goes in the back cup again, he gets a third and final yardage shot. If the third throw goes in any yardage cup, he gets one shot at the Hail Mary Cup for a breakaway touchdown.
On 4th down, the offense may choose to punt. A punt is automatically 25 yards, and the punting team gets one ping pong ball to throw for more yardage. The yardage cups from front row to back row are worth 5, 10, 15, 20 yards, repsectively, so that a punt can net a possible 45 yards. The returning team will have a chance to return the punt, it is the same as a kickoff return.
If a team is on the opponents 30 yard line or less, they may try a field goal. The field goal will be to flick the triangle football through the goal posts. If the ball is on the 30, then the flick will be from the team's own goal line, if the ball is on the 1, the flick will be from the team's own 29 yard line. Wherever the ball is on the field, the flick will be from 70 yards behind that point.
My friends and I never used a clock, we just picked a score to play to. We called it halftime when one team got past half the winning score. If you want to be hardcore, you could implement a play clock and everything, but we felt that would take too much fun out of it. If you really wanted to simulate time but not do that, maybe you could take a standard amount of time off the clock per play or something.