Haymaker
Mawashi tsuki (literally: “go-around punch”) is called a haymaker in English, since it mimes mowing grasses with an invisible scythe. Haymakers are derisively called "cowboy punches," since they were the staple of Western movie barfight scenes.
To perform a haymaker, whip your arm from the shoulder in a large horizontal loop. Unlike a conventional karate punch, haymakers do not “snap,” they use weight transfer to generate momentum, rather than using muscle contraction to deliver power. This requires a significant wind-up, which telegraphs the punch. To optimize your momentum, take a same-side step forward as your swing, like a pursuit punch. Unlike a hook punch, haymakers have little-to-no bend in the elbow, to optimize their range. You must turn your wrist slightly inward to ensure that your knuckles contact the opponent -- however, your seiken will not be in-line with your forearm, increasing your risk of suffering a sprained wrist or a boxer’s fracture. Because of their large semicircular path, haymakers must travel π-times longer than a straight punch would. Haymakers thus take over three times as long to connect than a straight punch would, giving even moderately-skilled opponents the time needed to evade, block, and counterattack.
For the reasons given above, haymakers are almost never used in karate, except when assuming the opponent's role during haymaker-defense waza. However, haymakers are extremely popular among untrained fighters (e.g., edgy middle schoolers, drunks outside of bars), because they look spectacular, feel powerful, and require literally no skill. Karateka must study haymakers to know how to stop haymakers, because if you are ever attacked, it will likely be with one of those.
{Video of Haymakers from the front and side}