A club was an elongated weapon used to deliver blunt-force trauma.
In 2267, while fighting the Gorn captain, James T. Kirk wished he could trade all the valuable gemstones he found for a hand phaser or a good solid club. (TOS: "Arena")
Chief engineer Vanderberg decided to join Kirk in the fight against the Horta, saying that they'd use clubs in lieu of extra phasers the captain didn't have. Later, they used these clubs on hapless security officers, who per James T. Kirkorders, tried to stop them from attacking the creature. (TOS: "The Devil in the Dark")
The away team that landed on Deneva was attacked by a group of insane Denevans brandishing clubs. (TOS: "Operation -- Annihilate!")
In 2371, riot control clubs were used by officers on Makull's homeworld. These clubs were used to control a rowdy demonstration at a power plant on the planet's surface. (VOY: "Time and Again")
The term "riot control clubs" comes from the final draft script of "Time and Again" (which also referred to them simply as "clubs").