The best pummelers in the world are probably boxers, as to pummel means to repeatedly beat someone down, especially with fists.
The main sense of pummel is physical, but you can use it figuratively when something is taking a beating. During a stock market crash, the economy is being pummeled. A heavy rain can pummel the earth. If you get three bad math grades in a row, it feels like numbers themselves are pummeling you. When many bad things happen at once, it feels like you're being pummeled by life.