I'm not sure how they'd include that in a contract, they'd need an objective opinion as to how he plays. He could easily dispute any claim that he played sub-par. Instead of 12.5k/goal we could give him around 1-2 million for hitting 15 goals in one season or something like that. That may work out cheaper for us, we won't have to pay him a thing should he fail to achieve our target, and it'll motivate him to try his best- not that he doesn't put in 100% every time he plays anyway.