In football, after every play, there’s a seemingly interminable period until the next play starts, during which they show replays and talk about what they just saw. The delay is even longer for plays involving flags, and perhaps just long enough:

They could set up a SMS number and show it on screen after every flag, asking the viewers to tell them whether or not they agreed with the referee’s call, charging 25 cents or more per vote. Then after a short while they could display the results on screen.

If there isn’t enough time to gather and calculate the results before the next play, they could just post random numbers that almost always favor the referee, encouraging those that disagree to vote the next time. It doesn’t matter if it’s accurate, and it might be better if it’s inaccurate.

Easy money.