When Cam Newton signed his five-year $103 million extension, the contract included his base salary and a signing bonus, but it also included several workout bonuses. The workout incentives were apparently designed to motivate Cam to spend his offseasons in the gym instead watching Netflix and eating Cheetos like the rest of us bums.
Outside of workout bonuses, most incentive payouts in NFL contracts are tied to traditional statistics like sacks, tackles, receptions, downs played, and not getting injured by a slippery fondue pot.
As a fan, my preference would be for incentive bonuses to be tied to plays that not only influence the outcome of the game, but are also just simply awesome to watch.