A good example of this is when defenders try to "blow up" a victory formation. It's perfectly legal, but generally considered bad sportsmanship.

This, and many other "bad sportsmanship" behaviors, are taboo because they are far less likely to affect the result of the game than they are to injure someone.

Behaviors like this will typically result in some variation of an on-field fight, which honestly seems like a pretty fair means of enforcement.

Not to mention that big money sports relies on spectatorship so you'll see adjustments to the rules to encourage exciting and offensive play. The English Premier League has adjusted rules over the years and ONE FC also attempts to encourage offensive action for fights.