Where one derives sexual pleasure from being struck on their buttocks, or other body parts, or by administrating such striking actions.
To inflict / receive pain, generally along the buttocks or inner / outer thighs, through use of various implements, such as a riding crop, paddle, whip, or even the bare hand. This can include other areas of the body, but is generally administered to the more fleshy areas, for health safety reasons.
NOTE - Improper or untrained 'impact play' can result in bodily harm, to vital organs.
Depending on the agreed upon terms, a person can give or receive impact play until a safe word is used to end the session, or when certain other conditions are met, such as the color of the flesh, turning to blue or a deep red, or when there is the appearance of deep welts, and even blood.
Usually the person receiving 'impact play' is immobilized, and care has to be taken when using whips and other flaying implements, in order to not incur wrapping (where the ends of the implement miss the intended mark, and reach beyond that mark)
Wide objects, such as paddles produce a different sensation when striking, than a thin object like a cane or riding crop. The wide objects produce a more 'thud' type of pain, while the thinner items create a more sharp tingling pain.
When using more advanced tools, such as whips, a great deal of care has to be shown, to avoid injuries that aren't considered pleasurable. It can also, if mis-used, cause injury to various body parts, such as the kidneys or liver. Proper SKILL is required to administer whippings, that are generally across the lower back below the shoulder blades, and along the buttocks.
Practice (Associated Acts): Less common practice include punching, face slapping, and other similar treatments, all in the goal of inflicting pain. In the more 'intense' scenarios, it is also a form of humiliation.
Noteworthy: Some forms of 'impact play' are considered forms of 'torture' and are illegal in some countries, even when consensual.
The Folsom Street Fair generally has public display of various 'impact play', mostly Flogging.
As far back as 1769, many Brothels specialized in 'impact play' for their customers. This generally involved spanking and/or flogging.