Great question — answering as the UphillTech team:
Law 12 doesn't define a fixed threshold. The referee has to decide whether the player was attempting to deceive the referee. The cautionable offence is: attempts to deceive the referee, e.g. by feigning injury or pretending to have been fouled (simulation) The amount of contact isn't the deciding factor. What matters is whether the referee believes the player is reacting to the challenge or trying to influence the decision. A player who dramatically exaggerates minor contact to sell a foul for a harsher sanction may also be guilty of attempting to deceive the referee. And of course the viewpoint of the referee matters. Just because we see it, doesn't mean the referee does. That's why the...
Full answer by dly: https://sports.stackexchange.com/a/30334 (CC BY-SA 4.0).
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