In professional sports both money and reputation can be on the line in every match, and so the ideals of sportsmanship can be tested to the breaking point. Even pro golf has had its cheating scandals.
In sports that feature rough physical contact, such as ice hockey or American football, a bigger issue is excessive violence; in the heat of battle, the limits on dangerous behaviour can easily be forgotten.
But the latest news from the National Football League, in the US, reflects an aspect of sport much darker than mere flare-ups of temper: during his service with two different teams, a defensive coordinator named Gregg Williams operated a system that paid cash to players who inflicted injuries that knocked opposing attackers out of games.
The New Orleans Saints and the Washington Redskins say higher management knew nothing of the scheme. But there is anecdotal evidence of similar, if less-organised, bounty systems on other clubs as well.
As in so many aspects of life, exposure is the beginning of reform.
It's all just one more reminder, in case anyone needed it, that for all their hero status, sports stars too can share the dark side of human nature.